[PATCH] jbd: embed j_commit_timer in journal struct

The kjournald timer is currently on the kernel thread's stack and the journal
structure points at it.  Save a pointer hop by moving the timer into the
journal structure.

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>