libfdt: fix fdt_stringlist_count()

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

[ DTC commit: e28eff5b787adb3f461d1653598818b2f1f25a73 ]
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>

lib/libfdt/fdt_ro.c

@@ -550,7 +550,7 @@ int fdt_stringlist_count(const void *fdt, int nodeoffset, const char *property)
 
 	list = fdt_getprop(fdt, nodeoffset, property, &length);
 	if (!list)
-		return -length;
+		return length;
 
 	end = list + length;