[PATCH] sched: null domains

Fix the last 2 places that directly access a runqueue's sched-domain and
assume it cannot be NULL.

That allows the use of NULL for domain, instead of a dummy domain, to signify
no balancing is to happen.  No functional changes.

Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>