drm/v3d: fix a NULL vs error pointer mixup

The drm_gem_shmem_create() returns error pointers and v3d_bo_create() is
also supposed to return error pointers.

Fixes: 40609d4820b2 ("drm/v3d: Use the new shmem helpers to reduce driver boilerplate.")
Signed-off-by: Dan Carpenter <[e-mail]>
Signed-off-by: Eric Anholt <[e-mail]>
Reviewed-by: Eric Anholt <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/20190321062731.GC21489@kadam

drivers/gpu/drm/v3d/v3d_bo.c

···
 	int ret;
 
 	shmem_obj = drm_gem_shmem_create(dev, unaligned_size);
-	if (!shmem_obj)
-		return NULL;
+	if (IS_ERR(shmem_obj))
+		return ERR_CAST(shmem_obj);
 	bo = to_v3d_bo(&shmem_obj->base);
 
 	ret = v3d_bo_create_finish(&shmem_obj->base);