[POWERPC] Add include of linux/of.h to os-area.c

os-area.c requires routines declared in linux/of.h, so should include it.
Signed-off-by: NMichael Ellerman <michael@ellerman.id.au>
Signed-off-by: NPaul Mackerras <paulus@samba.org>

arch/powerpc/platforms/ps3/os-area.c

@@ -25,6 +25,7 @@
 #include <linux/syscalls.h>
 #include <linux/ctype.h>
 #include <linux/lmb.h>
+#include <linux/of.h>
 
 #include <asm/prom.h>