arm/mxc: use gpiolib helper for gpio_to_irq

As all the users of gpio_to_irq() in static initializers have been
migrated to IMX_GPIO_TO_IRQ, we can start using the standard gpiolib
helper for gpio_to_irq().
Signed-off-by: NShawn Guo <shawn.guo@linaro.org>
Signed-off-by: NSascha Hauer <s.hauer@pengutronix.de>

arch/arm/plat-mxc/include/mach/gpio.h

@@ -32,8 +32,8 @@
 #define gpio_get_value		__gpio_get_value
 #define gpio_set_value		__gpio_set_value
 #define gpio_cansleep		__gpio_cansleep
+#define gpio_to_irq		__gpio_to_irq
 
-#define gpio_to_irq(gpio)	(MXC_GPIO_IRQ_START + (gpio))
 #define irq_to_gpio(irq)	((irq) - MXC_GPIO_IRQ_START)
 
 #endif