libfdt: fix fdt_stringlist_search()

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

[ DTC commit: daa75e8fa5942caa8e97931aed3a1ee0b7edd74b ]

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

lib/libfdt/fdt_ro.c

@@ -576,7 +576,7 @@ 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;