This fixes the bug that caused BUG_ON(!irqs_disabled()) to trigger in
run_posix_cpu_timers() on alpha/smp.  We didn't disable interrupts
properly before calling smp_percpu_timer_interrupt().

We *do* disable interrupts everywhere except this unfortunate
smp_percpu_timer_interrupt().  Fixed thus.
Signed-off-by: Linus Torvalds <torvalds@osdl.org>