RDMA/uverbs: Fix a NULL vs IS_ERR() bug

The uapi_get_object() function returns error pointers, it never returns
NULL.

Fixes: 149d3845f4 ("RDMA/uverbs: Add a method to introspect handles in a context")
Link: https://lore.kernel.org/r/YJ6Got+U7lz+3n9a@mwanda
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/core/uverbs_std_types_device.c

@@ -117,8 +117,8 @@ static int UVERBS_HANDLER(UVERBS_METHOD_INFO_HANDLES)(
 		return ret;
 
 	uapi_object = uapi_get_object(attrs->ufile->device->uapi, object_id);
-	if (!uapi_object)
-		return -EINVAL;
+	if (IS_ERR(uapi_object))
+		return PTR_ERR(uapi_object);
 
 	handles = gather_objects_handle(attrs->ufile, uapi_object, attrs,
 					out_len, &total);