gpio: merrifield: set default handler to be handle_bad_irq()

We switch the default handler to be handle_bad_irq() instead of
handle_simple_irq() (which was not correct anyway).

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>