drm/qxl: avoid dependency lock

qxl_bo_unref calls drm_gem_object_unreference_unlocked which
locks dev->struct_mutex. However this lock could be already
locked if the call came from qxl_gem_object_free.
As we don't need to call qxl_bo_ref/qxl_bo_unref cause
qxl_release_list_add will hold a reference by itself avoid
to call them and the possible deadlock.

Signed-off-by: Frediano Ziglio <fziglio@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/qxl/qxl_release.c

@@ -307,7 +307,7 @@ int qxl_alloc_surface_release_reserved(struct qxl_device *qdev,
 		idr_ret = qxl_release_alloc(qdev, QXL_RELEASE_SURFACE_CMD, release);
 		if (idr_ret < 0)
 			return idr_ret;
-		bo = qxl_bo_ref(to_qxl_bo(entry->tv.bo));
+		bo = to_qxl_bo(entry->tv.bo);
 
 		(*release)->release_offset = create_rel->release_offset + 64;
 
@@ -316,8 +316,6 @@ int qxl_alloc_surface_release_reserved(struct qxl_device *qdev,
 		info = qxl_release_map(qdev, *release);
 		info->id = idr_ret;
 		qxl_release_unmap(qdev, *release, info);
-
-		qxl_bo_unref(&bo);
 		return 0;
 	}