scripts: fix checkpatch.pl for changed license dir

As multiple LICENSES are shipped and no longer just LICENSE, modify the
OpenWrt tree detection in checkpatch.pl.

Signed-off-by: Paul Spooren <mail@aparcar.org>

scripts/checkpatch.pl

@@ -1113,7 +1113,7 @@ sub top_of_openwrt_tree {
 	my ($root) = @_;
 
 	my @tree_check = (
-		"BSDmakefile", "Config.in", "LICENSE", "Makefile", "README.md",
+		"BSDmakefile", "Config.in", "LICENSES", "Makefile", "README.md",
 		"feeds.conf.default", "include", "package", "rules.mk",
 		"scripts", "target", "toolchain", "tools"
 	);