checkpatch: reword long-line warning about commit-msg

Reword the warning to complain about line length 1st, since thats
whats actually tested.

Link: https://lkml.kernel.org/r/20230808033019.21911-3-jim.cromie@gmail.com
Cc: apw@canonical.com
Cc: joe@perches.com
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>