gpio/omap: fix wakeup_en register update in _set_gpio_wakeup()

There are two ways through which wakeup_en register can be programmed
using gpiolib APIs as shown below. It is seen that in the second case
in _set_gpio_wakeup(), even though bank->suspend_wakeup is updated
correctly, its value is not programmed in wakeup_en register. Fix this.

irq_set_type()->gpio_irq_type()->_set_gpio_triggering()->set_gpio_trigger()
irq_set_wake()->gpio_wake_enable()->_set_gpio_wakeup()

Signed-off-by: Tarun Kanti DebBarma <tarun.kanti@ti.com>
Reviewed-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>