watchdog: ziirave_wdt: Zero out only what's necessary

Instead of zeroing out all of the packet and then overwriting a
significant portion of those zeros via memcpy(), zero out only a
portion of the packet that is known to not contain any data.

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/20190812200906.31344-11-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

@@ -260,15 +260,14 @@ static int __ziirave_firm_write_pkt(struct watchdog_device *wdd,
 		return -EMSGSIZE;
 	}
 
-	memset(packet, 0, sizeof(packet));
-
 	/* Packet length */
 	packet[0] = len;
 	/* Packet address */
 	packet[1] = addr16 & 0xff;
 	packet[2] = (addr16 & 0xff00) >> 8;
 
 	memcpy(packet + 3, data, len);
+	memset(packet + 3 + len, 0, ZIIRAVE_FIRM_PKT_DATA_SIZE - len);
 
 	/* Packet checksum */
 	for (i = 0; i < len + 3; i++)