drm/etnaviv: add lockdep annotation for userptr object population

The current userptr page population will defer work to a work item if
needed to avoid ever taking the mmap_sem in the direct call path. With
the more fine-grained locking in etnaviv this isn't needed anymore, so
a future commit will simplify this code.

Add a lockdep annotation to validate the assumption that the mmap_sem
can be taken in the direct call path.
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>

drivers/gpu/drm/etnaviv/etnaviv_gem.c

@@ -804,6 +804,8 @@ static int etnaviv_gem_userptr_get_pages(struct etnaviv_gem_object *etnaviv_obj)
 	struct mm_struct *mm;
 	int ret, pinned, npages = etnaviv_obj->base.size >> PAGE_SHIFT;
 
+	might_lock_read(&current->mm->mmap_sem);
+
 	if (etnaviv_obj->userptr.work) {
 		if (IS_ERR(etnaviv_obj->userptr.work)) {
 			ret = PTR_ERR(etnaviv_obj->userptr.work);