checkpatch: fix detection of git repository

Since git v1.7.7, the .git directory can be a file when, for example,
the kernel is a submodule of another git super project.  So, the check
"-d .git" is not working anymore in this case.  Using a more generic
check like "-e .git" corrects this behaviour.
Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -471,7 +471,7 @@ sub seed_camelcase_includes {
 
 	$camelcase_seeded = 1;
 
-	if (-d ".git") {
+	if (-e ".git") {
 		my $git_last_include_commit = `git log --no-merges --pretty=format:"%h%n" -1 -- include`;
 		chomp $git_last_include_commit;
 		$camelcase_cache = ".checkpatch-camelcase.git.$git_last_include_commit";
@@ -499,7 +499,7 @@ sub seed_camelcase_includes {
 		return;
 	}
 
-	if (-d ".git") {
+	if (-e ".git") {
 		$files = `git ls-files "include/*.h"`;
 		@include_files = split('\n', $files);
 	}