ignore submodule updates in diff

this avoids that we blow up on submodule updates inside merges.

Change-Id: I5608554ae4991b379219199c32e2394c3a0b1518
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

git-hooks/sanitize-commit

@@ -472,7 +472,7 @@ my $tsv_check;
 my $eof_check;
 my $ctlkw_check;
 my $apple_check;
-open DIFF, "git diff-tree --patience --no-commit-id --diff-filter=ACMR --src-prefix=\@old\@/ --dst-prefix=\@new\@/ --full-index -r -U100000 --cc -C -l1000 --root ".$sha1." |" or die "cannot run git: $!";
+open DIFF, "git diff-tree --patience --no-commit-id --diff-filter=ACMR --ignore-submodules --src-prefix=\@old\@/ --dst-prefix=\@new\@/ --full-index -r -U100000 --cc -C -l1000 --root ".$sha1." |" or die "cannot run git: $!";
 while (<DIFF>) {
     if (/^-/) {
         if ($mixws_check) {