__handle_sysrq was modified to do a spin_lock_irqsave so we were entering
smp_send_stop with interrupts.  So reenable interrupts to prevent the
possible smp_call_function() deadlock.

(It's still deadlocky if the sysrq handler is against called via an
interrupt from a different device, but that seems unlikely).
Signed-off-by: Zwane Mwaikambo <zwane@holomorphy.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>