[POWERPC] bootwrapper: Use map_string() instead of lookup_string() in ft_prop().

When adding a property, the property name should be added to the string
table if it doesn't already exist.  map_string() does that;
lookup_string() will fail instead.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/boot/flatdevtree.c b/arch/powerpc/boot/flatdevtree.c
index f2a29ca..e319a65 100644
--- a/arch/powerpc/boot/flatdevtree.c
+++ b/arch/powerpc/boot/flatdevtree.c
@@ -429,7 +429,7 @@
 {
 	int off, len;
 
-	off = lookup_string(cxt, name);
+	off = map_string(cxt, name);
 	if (off == NO_STRING)
 		return -1;