drm/plane: Fix create_in_format_blob() return value

create_in_format_blob() is either supposed to return a valid
pointer or an error, but never NULL. The caller will dereference
the blob when it is not an error, and thus will oops if NULL
returned. Return proper error values in the failure cases.

Cc: [e-mail]
Cc: Arun R Murthy <[e-mail]>
Fixes: 0d6dcd741c26 ("drm/plane: modify create_in_formats to acommodate async")
Signed-off-by: Ville Syrjälä <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Reviewed-by: Arun R Murthy <[e-mail]>

drivers/gpu/drm/drm_plane.c

···
 	formats_size = sizeof(__u32) * plane->format_count;
 	if (WARN_ON(!formats_size)) {
 		/* 0 formats are never expected */
-		return 0;
+		return ERR_PTR(-EINVAL);
 	}
 
 	modifiers_size =
···
 
 	blob = drm_property_create_blob(dev, blob_size, NULL);
 	if (IS_ERR(blob))
-		return NULL;
+		return blob;
 
 	blob_data = blob->data;
 	blob_data->version = FORMAT_BLOB_CURRENT;