mips: Use the core irq stats function

Let the core do the irq_desc resolution.

No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: mips <inux-mips@linux-mips.org>
Link: http://lkml.kernel.org/r/20140223212737.517340416@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>