UPSTREAM: 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.

Signed-off-by: Wei Wang <wvw@google.com>
Acked-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Bug: 37158168
Test: checkpatch.pl --patch [diff] and no longer see failure
Change-Id: I65cf9a46874621dd6d5c349d2d3ca3b862d61ba3