[JFFS2] kill warning RE debug-only variables

gcc emits the following warning on a 'allmodconfig' build:

fs/jffs2/xattr.c: In function ‘unrefer_xattr_datum’:
fs/jffs2/xattr.c:402: warning: unused variable ‘version’
fs/jffs2/xattr.c:402: warning: unused variable ‘xid’

Given that these variables are only used in the debug printk, and they
merely remove a deref, we can easily kill the warning by adding the
derefs to the debug printk.

Signed-off-by: Jeff Garzik <jeff@garzik.org>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>