scripts/checkpatch.pl: fix git-show invocation to include diffstat

Without this checkpatch keeps complaining about new/changed files even
when MAINTAINERS has been updated. Normal invocations of checkpatch on
patch files rather than commit IDs are unaffected.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Willian Rampazzo <willianr@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210114165730.31607-13-alex.bennee@linaro.org>

scripts/checkpatch.pl

@@ -399,7 +399,7 @@ sub build_types {
 	my $num_patches = @patches;
 	for my $hash (@patches) {
 		my $FILE;
-		open($FILE, '-|', "git", "show", $hash) ||
+		open($FILE, '-|', "git", "show", "--patch-with-stat", $hash) ||
 			die "$P: git show $hash - $!\n";
 		while (<$FILE>) {
 			chomp;