mfd: wm8350 variable dereferenced before check

Remove "wm8350->irq_base = pdata->irq_base" to avoid
null pointer exception and wm8350->irq_base got from
irq_alloc_descs().

Signed-off-by: Jonghwan Choi <jhbird.choi@samsung.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>