tty: vt: simplify some unicode conditions

tty: vt: simplify some unicode conditions

After previous patches, we can simply test vc->vc_uni_lines, so do so in
many unicode functions. This makes the code more compact. And even use
  if (!)
    return;
in vc_uniscr_scroll(), so that the whole code is indented on the left.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20230112080136.4929-8-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>