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>

libfdt/fdt_ro.c

@@ -597,7 +597,7 @@ int fdt_stringlist_search(const void *fdt, int nodeoffset, const char *property,
 
 	list = fdt_getprop(fdt, nodeoffset, property, &length);
 	if (!list)
-		return -length;
+		return length;
 
 	len = strlen(string) + 1;
 	end = list + length;