serial: sc16is7xx: Read modem line state at startup

This patch sets the driver modem line state to the actual line state
at driver startup.

See: #5501

Signed-off-by: Earl Schmidt <schmidt.earl.f@gmail.com>
Signed-off-by: Phil Elwell <phil@raspberrypi.com>

drivers/tty/serial/sc16is7xx.c

@@ -1209,6 +1209,9 @@ static int sc16is7xx_startup(struct uart_port *port)
 	      SC16IS7XX_IER_MSI_BIT;
 	sc16is7xx_port_write(port, SC16IS7XX_IER_REG, val);
 
+	/* Initialize the Modem Control signals to current status */
+	one->old_mctrl = sc16is7xx_get_hwmctrl(port);
+
 	/* Enable modem status polling */
 	spin_lock_irqsave(&port->lock, flags);
 	sc16is7xx_enable_ms(port);