watchdog: ziirave_wdt: Fix JUMP_TO_BOOTLOADER payload

Bootloader firmware expects the following traffic for
JUMP_TO_BOOTLOADER:

S Addr Wr [A] 0x0c [A] 0x01 [A] P

using ziirave_firm_write_byte() will result in

S Addr Wr [A] 0x0c [A] 0x01 [A] 0x01 [A] P

which happens to work because firmware will ignore any extra bytes and
expected magic value matches byte count sent by
i2c_smbus_write_block_data(). Fix this by converting the code to use
i2c_smbus_write_byte_data() 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/20190812200906.31344-17-andrew.smirnov@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

drivers/watchdog/ziirave_wdt.c

@@ -72,6 +72,8 @@ static char *ziirave_reasons[] = {"power cycle", "hw watchdog", NULL, NULL,
 #define ZIIRAVE_CMD_JUMP_TO_BOOTLOADER		0x0c
 #define ZIIRAVE_CMD_DOWNLOAD_PACKET		0x0e
 
+#define ZIIRAVE_CMD_JUMP_TO_BOOTLOADER_MAGIC	1
+
 #define ZIIRAVE_FW_VERSION_FMT	"02.%02u.%02u"
 #define ZIIRAVE_BL_VERSION_FMT	"01.%02u.%02u"
 
@@ -376,8 +378,9 @@ static int ziirave_firm_upload(struct watchdog_device *wdd,
 	const struct ihex_binrec *rec;
 	int ret;
 
-	ret = ziirave_firm_write_byte(wdd, ZIIRAVE_CMD_JUMP_TO_BOOTLOADER, 1,
-				      false);
+	ret = i2c_smbus_write_byte_data(client,
+					ZIIRAVE_CMD_JUMP_TO_BOOTLOADER,
+					ZIIRAVE_CMD_JUMP_TO_BOOTLOADER_MAGIC);
 	if (ret) {
 		dev_err(&client->dev, "Failed to jump to bootloader\n");
 		return ret;