watchdog: ziirave_wdt: Fix DOWNLOAD_END payload

Bootloader firmware expects the following traffic for DOWNLOAD_END:

S Addr Wr [A] 0x11 [A] P

using ziirave_firm_write_byte() will result in

S Addr Wr [A] 0x11 [A] 0x01 [A] 0x01 [A] P

which happens to work because firmware will ignore any extra bytes
sent. Fix this by converting the code to use i2c_smbus_write_byte()
instead.
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Cc: Chris Healy <cphealy@gmail.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Rick Ramstetter <rick@anteaterllc.com>
Cc: linux-watchdog@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20190812200906.31344-18-andrew.smirnov@gmail.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

drivers/watchdog/ziirave_wdt.c

@@ -425,7 +425,7 @@ static int ziirave_firm_upload(struct watchdog_device *wdd,
 	}
 
 	/* End download operation */
-	ret = ziirave_firm_write_byte(wdd, ZIIRAVE_CMD_DOWNLOAD_END, 1, false);
+	ret = i2c_smbus_write_byte(client, ZIIRAVE_CMD_DOWNLOAD_END);
 	if (ret) {
 		dev_err(&client->dev,
 			"Failed to end firmware download: %d\n", ret);