wil6210: fix spurious interrupts in 3-msi

Interrupt is set in ICM (ICR & ~IMV) rising trigger.
As the driver masks the IRQ after clearing it, there can
be a race where an additional spurious interrupt is triggered
when the driver unmask the IRQ.
This can happen in case HW triggers an interrupt after the clear
and before the mask.

To prevent the second spurious interrupt the driver needs to mask the
IRQ before reading and clearing it.

Change-Id: Id72e6fed90b7b1a0322b82b58ce86ad8d03ebb54
Signed-off-by: Maya Erez <merez@codeaurora.org>