ARM: mach-imx: iomux-imx31: Staticize mxc_pin_alloc_map

Fix the following sparse warning:

arch/arm/mach-imx/iomux-imx31.c:43:15: warning: symbol 'mxc_pin_alloc_map' was not declared. Should it be static?
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/mach-imx/iomux-imx31.c

@@ -40,7 +40,7 @@ static DEFINE_SPINLOCK(gpio_mux_lock);
 
 #define IOMUX_REG_MASK (IOMUX_PADNUM_MASK & ~0x3)
 
-unsigned long mxc_pin_alloc_map[NB_PORTS * 32 / BITS_PER_LONG];
+static unsigned long mxc_pin_alloc_map[NB_PORTS * 32 / BITS_PER_LONG];
 /*
  * set the mode for a IOMUX pin.
  */