checkpatch: speed up checking for filenames in sections marked obsolete

Adding -f to the get_maintainer.pl invocation means git isn't invoked
by get_maintainer.pl for known filenames.

This reduces the overall time to run checkpatch.

Link: http://lkml.kernel.org/r/22991e3a295aeb399b43af0478b6e5809106ccee.1472684066.git.joe@perches.com
Signed-off-by: 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

@@ -759,7 +759,7 @@ sub is_maintained_obsolete {
 
 	return 0 if (!(-e "$root/scripts/get_maintainer.pl"));
 
-	my $status = `perl $root/scripts/get_maintainer.pl --status --nom --nol --nogit --nogit-fallback $filename 2>&1`;
+	my $status = `perl $root/scripts/get_maintainer.pl --status --nom --nol --nogit --nogit-fallback -f $filename 2>&1`;
 
 	return $status =~ /obsolete/i;
 }