drm/vc4: fix error code in vc4_create_object()

The ->gem_create_object() functions are supposed to return NULL if there
is an error.  None of the callers expect error pointers so returing one
will lead to an Oops.  See drm_gem_vram_create(), for example.

Fixes: c826a6e1 ("drm/vc4: Add a BO cache.")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20211118111416.GC1147@kili

drivers/gpu/drm/vc4/vc4_bo.c

@@ -391,7 +391,7 @@ struct drm_gem_object *vc4_create_object(struct drm_device *dev, size_t size)
 
 	bo = kzalloc(sizeof(*bo), GFP_KERNEL);
 	if (!bo)
-		return ERR_PTR(-ENOMEM);
+		return NULL;
 
 	bo->madv = VC4_MADV_WILLNEED;
 	refcount_set(&bo->usecnt, 0);