[ARM] pxa: fix incorrect mfp_to_gpio() conversion

Since MFP_PIN_GPIO* now includes 128-255, mfp_to_gpio() is no longer
valid for those additional pins, fix it.
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>

arch/arm/plat-pxa/include/plat/mfp.h

@@ -16,7 +16,7 @@
 #ifndef __ASM_PLAT_MFP_H
 #define __ASM_PLAT_MFP_H
 
-#define mfp_to_gpio(m)	((m) % 128)
+#define mfp_to_gpio(m)	((m) % 256)
 
 /* list of all the configurable MFP pins */
 enum {