FROMGIT: f2fs: fix missing check for f2fs_unlock_op

This fixes what Chao pointed. Upstream patch should be fine.

Fixes: 8c77bd62d6e4 ("f2fs: fix quota_sync failure due to f2fs_lock_op")
Change-Id: Ia697c8cf3897895392bbc0364d7d76f16ec9049e
Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>