serial: fix kernel-doc warnings in 8250.c

Fix kernel-doc warnings in drivers/tty/serial/8250/8250.c:

Warning(drivers/tty/serial/8250/8250.c:3128): No description found for parameter 'up'
Warning(drivers/tty/serial/8250/8250.c:3128): Excess function parameter 'port' description in 'serial8250_register_8250_port'

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>