gpio: max732x: Add IRQF_SHARED to irq flags

It's possible that multiple MAX732X can be hooked up to the same
interrupt line with the processor. So add IRQF_SHARED in requesting irq.

Signed-off-by: Semen Protsenko <semen.protsenko@globallogic.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>