mfd: Don't use NO_IRQ in WM8350

NO_IRQ is only defined on some architectures - the general way to test
for an invalid IRQ in the modern kernel is by comparing with zero.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@openedhand.com>