tty/serial: atmel: manage shutdown in case of RS485 or ISO7816 mode

In atmel_shutdown() we call atmel_stop_rx() and atmel_stop_tx() functions.
Prevent the rx restart that is implemented in RS485 or ISO7816 modes when
calling atmel_stop_tx() by using the atomic information tasklet_shutdown
that is already in place for this purpose.

Fixes: 98f2082c3ac4 ("tty/serial: atmel: enforce tasklet init and termination sequences")
Signed-off-by: Nicolas Ferre <[e-mail]>
Cc: stable <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/atmel_serial.c

···
 	atmel_uart_writel(port, ATMEL_US_IDR, atmel_port->tx_done_mask);
 
 	if (atmel_uart_is_half_duplex(port))
-		atmel_start_rx(port);
+		if (!atomic_read(&atmel_port->tasklet_shutdown))
+			atmel_start_rx(port);
 
 }