tty: atmel_serial: use the correct RTS flag.

tty: atmel_serial: use the correct RTS flag.

In RS485 mode, the RTS pin is driven high by hardware when the transmitter
is operating. This behaviour cannot be changed. This means that the driver
should claim that it supports SER_RS485_RTS_ON_SEND and not
SER_RS485_RTS_AFTER_SEND.

Otherwise, when configuring the port with the SER_RS485_RTS_ON_SEND, one
get the following warning:

kern.warning kernel: atmel_usart_serial atmel_usart_serial.2.auto:
ttyS1 (1): invalid RTS setting, using RTS_AFTER_SEND instead

which is contradictory with what's really happening.

Signed-off-by: Mathieu Othacehe <othacehe@gnu.org>
Cc: stable <stable@kernel.org>
Tested-by: Alexander Dahl <ada@thorsis.com>
Fixes: af47c491e3c7 ("serial: atmel: Fill in rs485_supported")
Link: https://lore.kernel.org/r/20240808060637.19886-1-othacehe@gnu.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>