pinctrl/samsung: Use irq_set_handler_locked()

Use irq_set_handler_locked() as it avoids a redundant lookup of the
irq descriptor.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: linux-gpio@vger.kernel.org