mmc: mxcmmc: explicitly includes mach/hardware.h

When indirect inclusion to <mach/hardware.h> via <mach/gpio.h> gets
removed, we will see the following compile error.

  CC      drivers/mmc/host/mxcmmc.o
drivers/mmc/host/mxcmmc.c: In function ‘mxcmci_init_card’:
drivers/mmc/host/mxcmmc.c:811:2: error: implicit declaration of function ‘cpu_is_mx3’
Signed-off-by: NShawn Guo <shawn.guo@linaro.org>
Signed-off-by: NSascha Hauer <s.hauer@pengutronix.de>

drivers/mmc/host/mxcmmc.c

@@ -40,6 +40,7 @@
 #include <mach/mmc.h>
 
 #include <mach/dma.h>
+#include <mach/hardware.h>
 
 #define DRIVER_NAME "mxc-mmc"