gpio/omap: fix _set_gpio_irqenable implementation

This function should be capable of both enabling and disabling interrupts
based upon the *enable* parameter. Right now the function only enables
the interrupt and *enable* is not used at all. So add the interrupt
disable capability also using the parameter.

Signed-off-by: Tarun Kanti DebBarma <tarun.kanti@ti.com>
Reviewed-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Felipe Balbi <balbi@ti.com>
Reviewed-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>