ocfs2: Move buckets up into ocfs2_add_new_xattr_cluster().

Lift the buckets from ocfs2_adjust_xattr_cross_cluster() up into
ocfs2_add_new_xattr_cluster().  Now ocfs2_adjust_xattr_cross_cluster()
doesn't deal with buffer_heads.

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