mfd: Ignore non-GPIO IRQs when setting wm831x IRQ types

The driver was originally tested with an additional patch which
made this unneeded but that patch had issuges and got lost on the
way to mainline, causing problems when the errors are reported.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
Cc: stable@kernel.org