x86: irq no should not use hex in /proc/interrupts

Arjan van de Ven noticed that we changed IRQ numbers from decimal
to hex in /proc/interrupts - that can break user-space utilities
like irqbalanced.

Reported-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>