watchdog: ziirave_wdt: Fix DOWNLOAD_START payload

Bootloader firmware expects the following traffic for DOWNLOAD_END:

S Addr Wr [A] 0x10 [A] P

using ziirave_firm_write_byte() will result in

S Addr Wr [A] 0x10 [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/20190812200906.31344-21-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

@@ -217,13 +217,6 @@ static int ziirave_firm_write_block_data(struct watchdog_device *wdd,
 	return ret;
 }
 
-static int ziirave_firm_write_byte(struct watchdog_device *wdd, u8 command,
-				   u8 byte, bool wait_for_ack)
-{
-	return ziirave_firm_write_block_data(wdd, command, 1, &byte,
-					     wait_for_ack);
-}
-
 static bool ziirave_firm_addr_readonly(u32 addr)
 {
 	return addr < ZIIRAVE_FIRM_FLASH_MEMORY_START ||
@@ -375,12 +368,18 @@ static int ziirave_firm_upload(struct watchdog_device *wdd,
 
 	msleep(500);
 
-	ret = ziirave_firm_write_byte(wdd, ZIIRAVE_CMD_DOWNLOAD_START, 1, true);
+	ret = i2c_smbus_write_byte(client, ZIIRAVE_CMD_DOWNLOAD_START);
 	if (ret) {
 		dev_err(&client->dev, "Failed to start download\n");
 		return ret;
 	}
 
+	ret = ziirave_firm_read_ack(wdd);
+	if (ret) {
+		dev_err(&client->dev, "No ACK for start download\n");
+		return ret;
+	}
+
 	msleep(500);
 
 	for (rec = (void *)fw->data; rec; rec = ihex_next_binrec(rec)) {