drm/amdgpu: Fix the use-after-free issue in wait IOCTL

The xarray pointer which has the userqueue xarray structure
reference should be cleared when the userqueue gets
destroyed. Otherwise, we may access the freed xa memory and
see the below warnings.

warning 1:
BUG: KASAN: slab-use-after-free in _raw_spin_lock+0x7a/0xe0
[  +0.000044] Call Trace:
[  +0.000017]  <TASK>
[  +0.000016]  dump_stack_lvl+0x6c/0x90
[  +0.000025]  print_report+0xc4/0x5e0
[  +0.000025]  ? srso_return_thunk+0x5/0x5f
[  +0.000024]  ? kasan_complete_mode_report_info+0x60/0x1d0
[  +0.000030]  ? _raw_spin_lock+0x7a/0xe0
[  +0.000023]  kasan_report+0xdf/0x120
[  +0.000023]  ? _raw_spin_lock+0x7a/0xe0
[  +0.000025]  kasan_check_range+0xf7/0x1b0
[  +0.000025]  __kasan_check_write+0x14/0x20
[  +0.000024]  _raw_spin_lock+0x7a/0xe0
[  +0.000023]  ? __pfx__raw_spin_lock+0x10/0x10
[  +0.000024]  ? amdgpu_userq_wait_ioctl+0xac0/0x1f30 [amdgpu]
[  +0.000442]  amdgpu_userq_wait_ioctl+0x18fc/0x1f30 [amdgpu]
[  +0.000428]  ? __pfx_amdgpu_userq_wait_ioctl+0x10/0x10 [amdgpu]
[  +0.000424]  ? __pfx_idr_alloc_u32+0x10/0x10
[  +0.000027]  ? srso_return_thunk+0x5/0x5f
[  +0.000024]  ? __kasan_check_write+0x14/0x20
[  +0.000025]  ? srso_return_thunk+0x5/0x5f
[  +0.000024]  ? idr_alloc+0x72/0xc0
[  +0.000023]  ? srso_return_thunk+0x5/0x5f
[  +0.000023]  ? fput+0x1c/0x2f0
[  +0.000025]  drm_ioctl_kernel+0x178/0x2f0 [drm]
[  +0.000065]  ? __pfx_amdgpu_userq_wait_ioctl+0x10/0x10 [amdgpu]
[  +0.000425]  ? __pfx_drm_ioctl_kernel+0x10/0x10 [drm]
[  +0.000064]  ? srso_return_thunk+0x5/0x5f
[  +0.000023]  ? __kasan_check_write+0x14/0x20
[  +0.000025]  drm_ioctl+0x513/0xd20 [drm]
[  +0.000058]  ? __pfx_amdgpu_userq_wait_ioctl+0x10/0x10 [amdgpu]
[  +0.000428]  ? __pfx_drm_ioctl+0x10/0x10 [drm]
[  +0.000061]  ? __pfx__raw_spin_lock_irqsave+0x10/0x10
[  +0.000027]  ? __count_memcg_events+0x11f/0x3a0
[  +0.000027]  ? srso_return_thunk+0x5/0x5f
[  +0.001040]  ? srso_return_thunk+0x5/0x5f
[  +0.000969]  ? _raw_spin_unlock_irqrestore+0x27/0x50
[  +0.000966]  amdgpu_drm_ioctl+0xcd/0x1d0 [amdgpu]
[  +0.001352]  __x64_sys_ioctl+0x135/0x1b0
[  +0.000966]  x64_sys_call+0x1205/0x20d0
[  +0.000968]  do_syscall_64+0x4d/0x120
[  +0.000960]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[  +0.000962] RIP: 0033:0x7f42af11a94f

warning 2:
WARNING: at lib/xarray.c:1849 __xa_alloc+0x13a/0x150
[  366.491409] RIP: 0010:__xa_alloc+0x13a/0x150
[  366.491434] Call Trace:
[  366.491437]  <TASK>
[  366.491440]  ? show_regs+0x6d/0x80
[  366.491445]  ? __warn+0x91/0x140
[  366.491450]  ? __xa_alloc+0x13a/0x150
[  366.491453]  ? report_bug+0x1c9/0x1e0
[  366.491459]  ? handle_bug+0x63/0xa0
[  366.491463]  ? exc_invalid_op+0x1d/0x80
[  366.491467]  ? asm_exc_invalid_op+0x1f/0x30
[  366.491476]  ? __xa_alloc+0x13a/0x150
[  366.491484]  amdgpu_userq_wait_ioctl+0xe0e/0xfe0 [amdgpu]
[  366.491743]  ? idr_alloc_u32+0x97/0xd0
[  366.491749]  ? __pfx_amdgpu_userq_wait_ioctl+0x10/0x10 [amdgpu]
[  366.491912]  drm_ioctl_kernel+0xae/0x100 [drm]
[  366.491942]  drm_ioctl+0x2a1/0x500 [drm]
[  366.491961]  ? __pfx_amdgpu_userq_wait_ioctl+0x10/0x10 [amdgpu]
[  366.492127]  ? srso_return_thunk+0x5/0x5f
[  366.492132]  ? srso_return_thunk+0x5/0x5f
[  366.492135]  ? _raw_spin_unlock_irqrestore+0x2b/0x50
[  366.492139]  amdgpu_drm_ioctl+0x4f/0x90 [amdgpu]
[  366.492288]  __x64_sys_ioctl+0x99/0xd0
[  366.492295]  x64_sys_call+0x1209/0x20d0
[  366.492299]  do_syscall_64+0x51/0x120
[  366.492303]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[  366.492418] RIP: 0033:0x7f86f3b1a94f

Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>