ARM: imx: fix missing include of common.h

Fix the following warning by including ../common.h to provide
the protoype for mxc_register_gpio() :

arch/arm/mach-imx/devices/platform-gpio-mxc.c:11:24: warning: symbol 'mxc_register_gpio' was not declared. Should it be static?
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/mach-imx/devices/platform-gpio-mxc.c

@@ -7,6 +7,7 @@
  * Free Software Foundation.
  */
 #include "devices-common.h"
+#include "../common.h"
 
 struct platform_device *__init mxc_register_gpio(char *name, int id,
 	resource_size_t iobase, resource_size_t iosize, int irq, int irq_high)