tty/serial: fix serial_core.c kernel-doc warnings

Fix kernel-doc warnings in serial_core.c:

../drivers/tty/serial/serial_core.c:3300: warning: Function parameter or member 'port' not described in 'uart_get_rs485_mode'
../drivers/tty/serial/serial_core.c:3300: warning: Excess function parameter 'dev' description in 'uart_get_rs485_mode'
../drivers/tty/serial/serial_core.c:3300: warning: Excess function parameter 'rs485conf' description in 'uart_get_rs485_mode'

Fixes: c150c0f3

 ("serial: Allow uart_get_rs485_mode() to return errno")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Lukas Wunner <lukas@wunner.de>
Cc: Heiko Stuebner <heiko@sntech.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-serial@vger.kernel.org
Link: https://lore.kernel.org/r/e170db8e-5c8b-27ac-79a4-81b96ac0ca2d@infradead.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>