gpio: 104-idio-16: Clear pending interrupt in IRQ handler

gpio: 104-idio-16: Clear pending interrupt in IRQ handler

The ACCES 104-IDIO-16 uses a single interrupt to indicate a possible
change-of-state in any of the digital input lines. As such, only a
single write to the device's "Clear Interrupt" register is necessary to
acknowledge the IRQ for all respective GPIO.

This patch moves the "Clear Interrupt" register write operation from the
irq_ack callback to the IRQ handler function, wherefore each interrupt
may be cleared respectively by executing a single outb call at the end
of the idio_16_irq_handler function, rather than multiple redundant outb
calls as a result of the generic_handle_irq call for each masked GPIO.

Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>