ubifs: ubifs_jnl_write_inode: Fix a memory leak bug

When inodes with extended attributes are evicted, xent is not freed in one
exit branch.

Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Fixes: 9ca2d732 ("ubifs: Limit number of xattrs per inode")
Signed-off-by: Richard Weinberger <richard@nod.at>