[media] rainshadow-cec: use strlcat instead of strncat

gcc warns about an obviously incorrect use of strncat():

drivers/media/usb/rainshadow-cec/rainshadow-cec.c: In function 'rain_cec_adap_transmit':
drivers/media/usb/rainshadow-cec/rainshadow-cec.c:299:4: error: specified bound 48 equals the size of the destination [-Werror=stringop-overflow=]

It seems that strlcat was intended here, and using that makes the
code correct.

Fixes: 0f314f6c ("[media] rainshadow-cec: new RainShadow Tech HDMI CEC driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/usb/rainshadow-cec/rainshadow-cec.c

@@ -296,7 +296,7 @@ static int rain_cec_adap_transmit(struct cec_adapter *adap, u8 attempts,
 			 cec_msg_destination(msg), msg->msg[1]);
 		for (i = 2; i < msg->len; i++) {
 			snprintf(hex, sizeof(hex), "%02x", msg->msg[i]);
-			strncat(cmd, hex, sizeof(cmd));
+			strlcat(cmd, hex, sizeof(cmd));
 		}
 	}
 	mutex_lock(&rain->write_lock);