media: hdpvr: add terminating 0 at end of string

dev->usbc_buf was passed as argument for %s, but it was not safeguarded
by a terminating 0.

This caused this syzbot issue:

https://syzkaller.appspot.com/bug?extid=79d18aac4bf1770dd050

Reported-and-tested-by: syzbot+79d18aac4bf1770dd050@syzkaller.appspotmail.com
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/usb/hdpvr/hdpvr-core.c

@@ -137,6 +137,7 @@ static int device_authorization(struct hdpvr_device *dev)
 
 	dev->fw_ver = dev->usbc_buf[1];
 
+	dev->usbc_buf[46] = '\0';
 	v4l2_info(&dev->v4l2_dev, "firmware version 0x%x dated %s\n",
 			  dev->fw_ver, &dev->usbc_buf[2]);