Revert r350841. I didn't realize that on this chip, reading the interrupt

Revert r350841.  I didn't realize that on this chip, reading the interrupt
status register clears pending interrupts.  By moving that code out of the
interrupt handler into a taskqueue task, I effectively created an interrupt
storm by returning from the handler with the interrupt source still active.

We'll have to find a different solution for this driver's need to sleep
in an ithread context.