sparc64: Fix build of timer_interrupt().

arch/sparc/kernel/time_64.c: In function ‘timer_interrupt’:
  arch/sparc/kernel/time_64.c:732: error: ‘struct kernel_stat’ has no member named ‘irqs’
  make[1]: *** [arch/sparc/kernel/time_64.o] Error 1

Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>