spmi: pmic-arb: cleanup unrequested irqs

We see a unmapped irqs trigger right around bootup. This could
likely be because the bootloader exited leaving the interrupts
in an unknown or unhandled state.  Ack and mask the interrupt
if one is found. A request_irq later will unmask it and also
setup proper mapping structures.

Change-Id: Icc2fc4f1bd9b3333e5856fce2daa5ba2b69e9a87
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>
[collinsd: fix checkpatch warning]
Signed-off-by: David Collins <collinsd@codeaurora.org>