ocfs2: Pin journal head before accessing jh->b_committed_data

This patch adds jbd_lock_bh_state() and jbd_unlock_bh_state() around accessses
to jh->b_committed_data.

Fixes oss bugzilla#1131
http://oss.oracle.com/bugzilla/show_bug.cgi?id=1131



Signed-off-by: Sunil Mushran <sunil.mushran@oracle.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>