m68knommu: fix compare race in sched related code

The interrupts must be disabled before considering the need resched
bit of the task struct and they have to be disabled before calling
schedule()

Signed-off-by: Sebastian Siewior <bigeasy@linutronix.de>
Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>