kernel: ext4: fix mb_cache_entry's e_refcnt leak in ext4_xattr_block_cache_find()

In the Linux kernel, the following vulnerability has been resolved: ext4: fix mbcacheentry's erefcnt leak in ext4xattrblockcachefind Syzbot reports a warning as follows: ============================================ WARNING: CPU: 0 PID: 5075 at fs/mbcache.c:419 mbcachedestroy+0x224/0x290 Modules...