Make sure we only return 1 from the interrupt handler if the interrupt actually was for us.  Fixes problems when the interrupt is shared.
Make sure we only return 1 from the interrupt handler if the interrupt
actually was for us.  Fixes problems when the interrupt is shared.

tested by stu@, ok mikeb@

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars