btrfs: Return EXDEV for cross file system snapshot

EXDEV seems an appropriate error if an operation fails bacause it
crosses file system boundaries.
Reviewed-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NKusanagi Kouichi <slash@ac.auone-net.jp>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

fs/btrfs/ioctl.c

@@ -1573,7 +1573,7 @@ static noinline int btrfs_ioctl_snap_create_transid(struct file *file,
 		if (src_inode->i_sb != file_inode(file)->i_sb) {
 			btrfs_info(BTRFS_I(src_inode)->root->fs_info,
 				   "Snapshot src from another FS");
-			ret = -EINVAL;
+			ret = -EXDEV;
 		} else if (!inode_owner_or_capable(src_inode)) {
 			/*
 			 * Subvolume creation is not restricted, but snapshots