pinctrl: at91: use locked variant of irq_set_handler

When setting the gpio irq type, use the __irq_set_handler_locked()
variant instead of the irq_set_handler() to prevent false
spinlock recursion warning.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: stable <stable@vger.kernel.org> # v3.12
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>