at91 gpio: fix typo in compatibility macro

It's called _pio_ in the version that was added to git.
Apparently it got renamed without updating the macros before it was
applied, c.f.
http://u-boot.10912.n7.nabble.com/U-Boot-PATCH-3-9-V3-add-a-new-AT91-GPIO-driver-td75922.html

Signed-off-by: Andreas Henriksson <andreas.henriksson@endian.se>
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>

arch/arm/include/asm/arch-at91/gpio.h

@@ -214,7 +214,7 @@ static inline unsigned pin_to_mask(unsigned pin)
 
 /* The following macros are need for backward compatibility */
 #define at91_set_GPIO_periph(x, y) \
-	at91_set_gpio_periph((x - PIN_BASE) / 32,(x % 32), y)
+	at91_set_pio_periph((x - PIN_BASE) / 32,(x % 32), y)
 #define at91_set_A_periph(x, y) \
 	at91_set_a_periph((x - PIN_BASE) / 32,(x % 32), y)
 #define at91_set_B_periph(x, y) \