[media] cec: fix ioctl return code when not registered

Don't return the confusing -EIO error code when the device is not registered,
instead return -ENODEV which is the proper thing to do in this situation.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/staging/media/cec/cec-api.c

@@ -435,7 +435,7 @@ static long cec_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 	void __user *parg = (void __user *)arg;
 
 	if (!devnode->registered)
-		return -EIO;
+		return -ENODEV;
 
 	switch (cmd) {
 	case CEC_ADAP_G_CAPS: