serial/arc-uart: Miscll DT related updates (Grant's review comments)

-replace "baud" with "current-speed"
-if uart alias doesn't exist in DT, don't abort, pick 0

Signed-off-by: Vineet Gupta <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Grant Likely <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: [e-mail]
Cc: Rob Herring <[e-mail]>
Cc: Rob Landley <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/devicetree/bindings/tty/serial/arc-uart.txt

···
 - reg			: offset and length of the register set for the device.
 - interrupts		: device interrupt
 - clock-frequency	: the input clock frequency for the UART
-- baud			: baud rate for UART
+- current-speed		: baud rate for UART
 
 e.g.
 
···
 	reg = <0xc0fc1000 0x100>;
 	interrupts = <5>;
 	clock-frequency = <80000000>;
-	baud = <115200>;
+	current-speed = <115200>;
 	status = "okay";
 };
 

drivers/tty/serial/arc_uart.c

···
 		}
 		uart->port.uartclk = val;
 
-		if (of_property_read_u32(np, "baud", &val)) {
-			dev_err(&pdev->dev, "baud property NOT set\n");
+		if (of_property_read_u32(np, "current-speed", &val)) {
+			dev_err(&pdev->dev, "current-speed property NOT set\n");
 			return -EINVAL;
 		}
 		uart->baud = val;
···
 		return -ENODEV;
 
 	dev_id = of_alias_get_id(np, "serial");
-	if (dev_id < 0) {
-		dev_err(&pdev->dev, "failed to get alias id: %d\n", dev_id);
-		return dev_id;
-	}
+	if (dev_id < 0)
+		dev_id = 0;
 
 	rc = arc_uart_init_one(pdev, dev_id);
 	if (rc)