[JFFS2][XATTR] Fix ACL bug when updating null xattr by null ACL.

This patch enable to handle the case when updating null xattr
by null ACL.

When we try to set NULL into NULL xattr, xattr subsystem returns
-ENODATA. This patch enables to handle this error code.

[2/3] jffs2-xattr-v6-02-fix_posixacl_bug.patch

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