checkpatch: use proper way for show problematic line

Instead of using an unnecessarily complicated approach to print a line
that is warned about, use `$herecurr` instead, just like everywhere else
in checkpatch.

While at it, remove a superfluous space in one of the changed lines, too. 
In a unmodified line also remove a superfluous check for a space before a
signed-off-by tag, to me consistent with the check at the start of the
section.

All three problems were found by Joe Perches during review of new code
inspired by the code modified here.

Link: https://lkml.kernel.org/r/a6d455c5196219b2095c2ac3645498052845f32e.1674217480.git.linux@leemhuis.info


Signed-off-by: Thorsten Leemhuis <linux@leemhuis.info>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Dwaipayan Ray <dwaipayanray1@gmail.com>
Cc: Joe Perches <joe@perches.com>
Cc: Kai Wasserbäch <kai@dev.carbon-project.org>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>