mfd: Apply irq_mask_cur before handling max77686 interrupts

According to TRM, though we mask the interrupts in interrupt-mask register,
interrupt source-register still provide the status of the masked interrupts.
So we should apply irq_mask_cur to read interrupt source-register value before
handling.

Signed-off-by: Yadwinder Singh Brar <yadi.brar@samsung.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>