[JFFS2][XATTR] Fix memory leak with jffs2_xattr_ref

If xattr_ref is associated with an orphan inode_cache
on filesystem mounting, those xattr_refs are not
released even if this inode_cache is released.

This patch enables to call jffs2_xattr_delete_inode()
for such a irregular inode_cachde too.

Signed-off-by: KaiGai Kohei <kaigai@ak.jp.nec.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>