libfdt: fix fdt_stringlist_search()

If fdt_getprop() fails, negative error code should be returned.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
diff --git a/libfdt/fdt_ro.c b/libfdt/fdt_ro.c
index db8d10f..3d00d2e 100644
--- a/libfdt/fdt_ro.c
+++ b/libfdt/fdt_ro.c
@@ -597,7 +597,7 @@
 
 	list = fdt_getprop(fdt, nodeoffset, property, &length);
 	if (!list)
-		return -length;
+		return length;
 
 	len = strlen(string) + 1;
 	end = list + length;