i386: Do not include other cpus' interrupt 0 in nmi_watchdog

kstat_irqs(0) includes the count of interrupt 0 from all cpus, not just
the current cpu.  The updated interrupt 0 on other cpus can stop the
nmi_watchdog from tripping, so only include the current cpu's int 0.

Signed-off-by: Keith Owens <kaos@ocs.com.au>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>