checkpatch: special audit for revert commit line

Currently checkpatch.pl does not recognize git's default commit revert
message and will complain about the hash format.  Add special audit for
revert commit message line to fix it.

Link: http://lkml.kernel.org/r/20170411191532.74381-1-wvw@google.com
Signed-off-by: Wei Wang <wvw@google.com>
Acked-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 3e2d9b0..b1befa2 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -2539,6 +2539,7 @@
 # Check for git id commit length and improperly formed commit descriptions
 		if ($in_commit_log && !$commit_log_possible_stack_dump &&
 		    $line !~ /^\s*(?:Link|Patchwork|http|https|BugLink):/i &&
+		    $line !~ /^This reverts commit [0-9a-f]{7,40}/ &&
 		    ($line =~ /\bcommit\s+[0-9a-f]{5,}\b/i ||
 		     ($line =~ /(?:\s|^)[0-9a-f]{12,40}(?:[\s"'\(\[]|$)/i &&
 		      $line !~ /[\<\[][0-9a-f]{12,40}[\>\]]/i &&