drm/amdgpu: error out on entity with no run queue

Disabled HW IP's entity initialized with NULL rq. We should not
process any submit request from userspace for a disabled HW IP.

Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>