scripts/checkpatch.pl: fix root dir detection and enable it

Don't try to find files specific for linux kernel.

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>

.checkpatch.conf

@@ -1,5 +1,4 @@
 --mailback
---no-tree
 --emacs
 --summary-file
 --show-types

scripts/checkpatch.pl

@@ -1016,9 +1016,9 @@ sub top_of_kernel_tree {
 	my ($root) = @_;
 
 	my @tree_check = (
-		"COPYING", "CREDITS", "Kbuild", "Makefile",
-		"README", "Documentation", "arch", "include", "drivers",
-		"fs", "init", "ipc", "kernel", "lib", "scripts",
+		"LICENSE", "CODEOWNERS", "Kconfig", "Makefile",
+		"README.rst", "doc", "arch", "include", "drivers",
+		"boards", "kernel", "lib", "scripts",
 	);
 
 	foreach my $check (@tree_check) {