sc16is7xx: don't wipe out port configuration on shutdown

EFCR register contains RS-485 configuration which should not
be changed by shutdown.  Instead of doing a write only update
the appropriate bits.
Signed-off-by: NJakub Kicinski <kubakici@wp.pl>
Signed-off-by: NJon Ringle <jringle@gridpoint.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sc16is7xx.c

@@ -903,9 +903,11 @@ static void sc16is7xx_shutdown(struct uart_port *port)
 	/* Disable all interrupts */
 	sc16is7xx_port_write(port, SC16IS7XX_IER_REG, 0);
 	/* Disable TX/RX */
-	sc16is7xx_port_write(port, SC16IS7XX_EFCR_REG,
-			     SC16IS7XX_EFCR_RXDISABLE_BIT |
-			     SC16IS7XX_EFCR_TXDISABLE_BIT);
+	sc16is7xx_port_update(port, SC16IS7XX_EFCR_REG,
+			      SC16IS7XX_EFCR_RXDISABLE_BIT |
+			      SC16IS7XX_EFCR_TXDISABLE_BIT,
+			      SC16IS7XX_EFCR_RXDISABLE_BIT |
+			      SC16IS7XX_EFCR_TXDISABLE_BIT);
 
 	sc16is7xx_power(port, 0);
 }