ocfs2: fix NULL pointer dereference in ocfs2_abort_trigger()

In the Linux kernel, the following vulnerability has been resolved:

ocfs2: fix NULL pointer dereference in ocfs2_abort_trigger()

bdev->bd_super has been removed and commit 8887b94d9322 change the usage
from bdev->bd_super to b_assoc_map->host->i_sb. Since ocfs2 hasn't set
bh->b_assoc_map, it will trigger NULL pointer dereference when calling
into ocfs2_abort_trigger().

Actually this was pointed out in history, see commit 74e364ad1b13. But
I've made a mistake when reviewing commit 8887b94d9322 and then
re-introduce this regression.

Since we cannot revive bdev in buffer head, so fix this issue by
initializing all types of ocfs2 triggers when fill super, and then get the
specific ocfs2 trigger from ocfs2_caching_info when access journal.

[joseph.qi@linux.alibaba.com: v2]