serial: sc16is7xx: Clear RS485 bits in the shutdown

We tested RS485 function on an EVB which has SC16IS752, after
finishing the test, we started the RS232 function test, but found the
RTS is still working in the RS485 mode.

That is because both startup and shutdown call port_update() to set
the EFCR_REG, this will not clear the RS485 bits once the bits are set
in the reconf_rs485(). To fix it, clear the RS485 bits in shutdown.

Cc: <stable@vger.kernel.org>
Signed-off-by: Hui Wang <hui.wang@canonical.com>
Link: https://lore.kernel.org/r/20220308110042.108451-1-hui.wang@canonical.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: jason77-wang

drivers/tty/serial/sc16is7xx.c

@@ -1238,10 +1238,12 @@ static void sc16is7xx_shutdown(struct uart_port *port)
 
 	/* Disable all interrupts */
 	sc16is7xx_port_write(port, SC16IS7XX_IER_REG, 0);
-	/* Disable TX/RX */
+	/* Disable TX/RX, clear auto RS485 and RTS invert */
 	sc16is7xx_port_update(port, SC16IS7XX_EFCR_REG,
 			      SC16IS7XX_EFCR_RXDISABLE_BIT |
-			      SC16IS7XX_EFCR_TXDISABLE_BIT,
+			      SC16IS7XX_EFCR_TXDISABLE_BIT |
+			      SC16IS7XX_EFCR_AUTO_RS485_BIT |
+			      SC16IS7XX_EFCR_RTS_INVERT_BIT,
 			      SC16IS7XX_EFCR_RXDISABLE_BIT |
 			      SC16IS7XX_EFCR_TXDISABLE_BIT);