ocfs2: fix NULL pointer dereference in function ocfs2_abort_trigger()

ocfs2_abort_trigger() use bh->b_assoc_map to get sb.  But there's no
function to set bh->b_assoc_map in ocfs2, it will trigger NULL pointer
dereference while calling this function.  We can get sb from
bh->b_bdev->bd_super instead of b_assoc_map.

[akpm@linux-foundation.org: update comment, per Joseph]
Signed-off-by: Njoyce.xue <xuejiufei@huawei.com>
Cc: Joseph Qi <joseph.qi@huawei.com>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/ocfs2/journal.c

@@ -571,9 +571,7 @@ static void ocfs2_abort_trigger(struct jbd2_buffer_trigger_type *triggers,
 	     (unsigned long)bh,
 	     (unsigned long long)bh->b_blocknr);
 
-	/* We aren't guaranteed to have the superblock here - but if we
-	 * don't, it'll just crash. */
-	ocfs2_error(bh->b_assoc_map->host->i_sb,
+	ocfs2_error(bh->b_bdev->bd_super,
 		    "JBD2 has aborted our journal, ocfs2 cannot continue\n");
 }