JFS: commit_mutex cleanups

I look at code, and see that
1)locks wasn't release in the opposite order in which they were taken
2)in jfs_rename we lock new_ip, and in "error path" we didn't unlock it
3)I see strange expression: "! !"

May be this worth to fix?

Signed-off-by: Evgeniy Dushistov <dushistov@mail.ru>
Signed-off-by: Dave Kleikamp <shaggy@austin.ibm.com>