tty/serial: atmel: reschedule TX after RX was started

tty/serial: atmel: reschedule TX after RX was started

When half-duplex RS485 communication is used, after RX is started, TX
tasklet still needs to be  scheduled tasklet. This avoids console freezing
when more data is to be transmitted, if the serial communication is not
closed.

Fixes: 01021bcec434 ("tty/serial: atmel: RS485 HD w/DMA: enable RX after TX is stopped")
Signed-off-by: Razvan Stefanescu <razvan.stefanescu@microchip.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20190813074025.16218-1-razvan.stefanescu@microchip.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>