drm/amdgpu/userq: use consistent function naming

s/userqueue/userq/

1. remove the mix of amdgpu_userqueue and amdgpu_userq
2. to be consistent with other amdgpu_userq_fence.c
3. it's shorter

Reviewed-by: Prike Liang <Prike.Liang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>