sparc64: Fix build by using kstat_irqs_cpu()

Changeset d7e51e66 ("sparseirq: make
some func to be used with genirq") broke the build on sparc64:

arch/sparc/kernel/irq_64.c: In function ‘show_interrupts’:
arch/sparc/kernel/irq_64.c:188: error: ‘struct kernel_stat’ has no member named ‘irqs’
make[1]: *** [arch/sparc/kernel/irq_64.o] Error 1

Fix by using the kstat_irqs_cpu() interface.

Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>