mx23: Fix pad voltage selection bit

On mx23 the pad voltage selection bit needs to be always '0', since '1' is a
reserved value.

For example:

Pin 108, EMI_A06 pin voltage selection:
0= 1.8V (mDDR) or 2.5V (DDR1);
1= reserved.

Fix the pad voltage definitions for the mx23 case.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Marek Vasut <marex@denx.de>

arch/arm/include/asm/arch-mxs/iomux.h

@@ -71,7 +71,11 @@ typedef u32 iomux_cfg_t;
 #define PAD_16MA		3
 
 #define PAD_1V8			0
+#if defined(CONFIG_MX28)
 #define PAD_3V3			1
+#else
+#define PAD_3V3			0
+#endif
 
 #define PAD_NOPULL		0
 #define PAD_PULLUP		1