TTY: 68328serial, use tty_port_block_til_ready

Since the code is identical, use the tty_port_block_til_ready helper
instead of re-implemented variant.

The code does not perform rtsdts handling, hence we do not need to
provide tty port hooks for them. The default ones will be used
instead. The only necessary thing is to provide tty_port_operations.
It is empty, but has to be there...

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: linux-m68k@lists.linux-m68k.org
Acked-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>