ocfs2: Specify appropriate journal access for new xattr buckets.

There are a couple places that get an xattr bucket that may be reading
an existing one or may be allocating a new one.  They should specify the
correct journal access mode depending.

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>