gpio: omap: add missed spin_unlock_irqrestore in omap_gpio_irq_type

Add missed spin_unlock_irqrestore in omap_gpio_irq_type when
omap_set_gpio_triggering() is failed.

It fixes static checker warning:

	drivers/gpio/gpio-omap.c:523 omap_gpio_irq_type()
	warn: inconsistent returns 'spin_lock:&bank->lock'.

This fixes commit:
1562e461 ('gpio: omap: fix error handling in omap_gpio_irq_type')

Reported-by: Javier Martinez Canillas <javier@dowhile0.org>
Signed-off-by: Grygorii Strashko <grygorii.strashko@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>