qemu-armv7: 32/64

This really is not critical but we might as well get it right.

Change-Id: Ifec1e8dc35d7f5bb89d9a7a877d82410c83a3288
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: http://review.coreboot.org/7070
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Tested-by: build bot (Jenkins)

src/mainboard/emulation/qemu-armv7/mmio.c

@@ -15,7 +15,7 @@
 
 #define VEXPRESS_UART0_IO_ADDRESS      (0x10009000)
 
-unsigned int uart_platform_base(int idx)
+uintptr_t uart_platform_base(int idx)
 {
 	return VEXPRESS_UART0_IO_ADDRESS;
 }