powerpc: fix build error in rom.c

Add missing include in rom.c. Fixes this build error when CONFIG_MTD=y:

arch/powerpc/sysdev/rom.c:26: error: implicit declaration of function of_platform_device_create

---
 arch/powerpc/sysdev/rom.c |    1 +
 1 files changed, 1 insertion(+)

@@ -9,6 +9,7 @@
 
 #include <linux/kernel.h>
 #include <asm/of_device.h>
+#include <asm/of_platform.h>
 
 static int __init powerpc_flash_init(void)
 {

Hello.

Uh oh, that's what happens when someone doesn't respin the patches quickly
enough. Finally, the obsolete version has been committed -- it also misses one property in the node spec and "reg" was called "regs" there...