checkpatch: if no filenames then read stdin

If no filenames are given, then read the patch from stdin.

Link: http://lkml.kernel.org/r/a8784f291ccb5067361992bf5d41ff6cfb0ce5cb.1469830917.git.allenbh@gmail.com
Signed-off-by: Allen Hubbe <allenbh@gmail.com>
Acked-by: Joe Perches <joe@perches.com>
Cc: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -228,9 +228,9 @@ if ($^V && $^V lt $minimum_perl_version) {
 	}
 }
 
+#if no filenames are given, push '-' to read patch from stdin
 if ($#ARGV < 0) {
-	print "$P: no input files\n";
-	exit(1);
+	push(@ARGV, '-');
 }
 
 sub hash_save_array_words {