drm/amdgpu: Fix amdgpu_userq_wait_ioctl() warn missing error code 'r'

To resolve the warning regarding the missing error code 'r' in
amdgpu_userq_wait_ioctl(), assign the value 'r = -EINVAL'.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202505080458.rnV8YfiY-lkp@intel.com/


Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Reviewed-by: Sunil Khatri <sunil.khatri@amd.com>
Signed-off-by: Arvind Yadav <Arvind.Yadav@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>