new helper: file_inode(file)

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 5445454..f80df6b 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -4542,7 +4542,7 @@
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	send_root = BTRFS_I(fdentry(mnt_file)->d_inode)->root;
+	send_root = BTRFS_I(file_inode(mnt_file))->root;
 	fs_info = send_root->fs_info;
 
 	arg = memdup_user(arg_, sizeof(*arg));