drm/amdgpu: remove set but not used variable 'priority'

drivers/gpu/drm/amd/amdgpu/amdgpu_job.c: In function amdgpu_job_submit:
drivers/gpu/drm/amd/amdgpu/amdgpu_job.c:148:26: warning: variable priority set but not used [-Wunused-but-set-variable]

commit 33abcb1f ("drm/amdgpu: set compute queue priority at mqd_init")
left behind this, remove it.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>