mfd: WM8350 off by one bug

If irq == WM8350_NUM_IRQ that would put us past the end of the array.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>