[JFFS2][XATTR] Handling the duplicate JFFS2_NODETYPE_XATTR node cases.

When jffs2_sum_process_sum_data() found a JFFS2_NODETYPE_XATTR
which has duplicate xid and older version, an error was returned
without appropriate process.
In the result, mounting filesystem is failed.

This patch fix this problem. If jffs2_setup_xattr_datum() returned
-EEXIST, the caller marks this node as DIRTY_SPACE().

[1/2] jffs2-xattr-v5.2-01-fix-duplicate-xdatum.patch

Signed-off-by: KaiGai Kohei <kaigai@ak.jp.nec.com>