drm/amdgpu/userq: fix error handling of invalid doorbell

If the doorbell is invalid, be sure to set the r to an error
state so the function returns an error.

Reviewed-by: David (Ming Qiang) Wu <David.Wu3@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c

@@ -471,6 +471,7 @@ amdgpu_userq_create(struct drm_file *filp, union drm_amdgpu_userq *args)
 	if (index == (uint64_t)-EINVAL) {
 		drm_file_err(uq_mgr->file, "Failed to get doorbell for queue\n");
 		kfree(queue);
+		r = -EINVAL;
 		goto unlock;
 	}