serial: 8250: drop DEBUG_AUTOCONF() macro

DEBUG_AUTOCONF() is always disabled (by "#if 0"), so one would need to
recompile the kernel to use it. And even if they did, they would find
out it is broken anyway:
  error: variable 'scratch' is used uninitialized whenever 'if' condition is false

Drop it.

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20250611100319.186924-30-jirislaby@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>