ext4: unlock on error in ext4_expand_extra_isize()

We need to unlock the xattr before returning on this error path.

Cc: stable@kernel.org # 4.13
Fixes: c03b45b8

 ("ext4, project: expand inode extra size if possible")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20191213185010.6k7yl2tck3wlsdkt@kili.mountain
Signed-off-by: Theodore Ts'o <tytso@mit.edu>