util/lint/checkpatch: Decrease commit message line length limit to 72

util/lint/checkpatch: Decrease commit message line length limit to 72

Currently, `checkpatch.pl`, imported from the Linux project, checks for
75 characters per line [2]:

> Suggest line wrapping at 75 columns so the default git commit log
> indentation of 4 plus the commit message text still fits on an 80
> column screen.

But Gerrit’s Web interface and its commit hooks use with 72 characters
per line [2]:

    remote: commit 35bb56d: warning: too many message lines longer than 72 characters; manually wrap lines
    remote:
    remote: SUCCESS
    remote:
    remote:   https://review.coreboot.org/c/coreboot/+/60004 [DO NOT SUBMIT] Gerrit commit msg line length test [NEW]

So, decrease the suggested length from 75 to 72 characters per line.

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2a076f40d8c9be95bee7bcf18436655e1140447f
[2]: https://review.coreboot.org/60004

Change-Id: Ic9c686cb1a902259b18377b76b5c999e94660fed
Signed-off-by: Paul Menzel <pmenzel@molgen.mpg.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60006
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>