m68k: Fall back to __gpio_to_irq() for non-arch GPIOs

gpiolib provides __gpio_to_irq() to map gpiolib gpios to interrupts - hook
that up on m68k.
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Greg Ungerer <gerg@uclinux.org>

arch/m68k/include/asm/gpio.h

@@ -225,7 +225,8 @@ static inline void gpio_set_value(unsigned gpio, int value)
 
 static inline int gpio_to_irq(unsigned gpio)
 {
-	return (gpio < MCFGPIO_IRQ_MAX) ? gpio + MCFGPIO_IRQ_VECBASE : -EINVAL;
+	return (gpio < MCFGPIO_IRQ_MAX) ? gpio + MCFGPIO_IRQ_VECBASE
+		: __gpio_to_irq(gpio);
 }
 
 static inline int irq_to_gpio(unsigned irq)