gpio: max732x: Fix irq-events handler

MAX732X clears all pending interrupts on I2C read (when interrupts
register is being read). Driver doesn't need to send any ACKs when
interrupt was handled. So replace handle_edge_irq() with
handle_simple_irq().

Using handle_edge_irq() (w/o .irq_ack callback set) may lead to NULL
pointer dereference in some cases. E.g. this was observed on
hibernation process:

  Unable to handle kernel NULL pointer dereference at virtual address 0
  Backtrace:
  (handle_edge_irq) from (resend_irqs)
  (resend_irqs) from (tasklet_action)
  (tasklet_action) from (__do_softirq)
  (__do_softirq) from (run_ksoftirqd)
  (run_ksoftirqd) from (smpboot_thread_fn)
  (smpboot_thread_fn) from (kthread)
  (kthread) from (ret_from_fork)

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

drivers/gpio/gpio-max732x.c

@@ -528,7 +528,7 @@ static int max732x_irq_setup(struct max732x_chip *chip,
 		ret =  gpiochip_irqchip_add(&chip->gpio_chip,
 					    &max732x_irq_chip,
 					    irq_base,
-					    handle_edge_irq,
+					    handle_simple_irq,
 					    IRQ_TYPE_NONE);
 		if (ret) {
 			dev_err(&client->dev,