m68knommu: 5772: Replace private irq flow handler

That handler lacks the minimal checks for action being zero etc. Keep
the weird flow - ack before handling - intact and call into
handle_simple_irq which does the right thing.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Greg Ungerer <gerg@uclinux.org>
LKML-Reference: <20110202212552.413849952@linutronix.de>
Signed-off-by: Greg Ungerer <gerg@uclinux.org>