Char: moxa, remove port->port

We don't need to hold a reference to port index.  In most cases we need port
structure anyway and index is available in port->tty->index.
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Tested-by: Oyvind Aabling <Oyvind.Aabling@uni-c.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>