[media] rc: unlock on error in show_protocols()

We recently introduced a new return -ENODEV in this function but we need
to unlock before returning.

[mchehab@redhat.com: found two patches with the same fix. Merged SOB's/acks into one patch]
Acked-by: Herton R. Krzesinski <herton.krzesinski@canonical.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: stable@vger.kernel.org
Signed-off-by: Douglas Bagnall <douglas@paradise.net.nz>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/rc/rc-main.c

@@ -789,8 +789,10 @@ static ssize_t show_protocols(struct device *device,
 	} else if (dev->raw) {
 		enabled = dev->raw->enabled_protocols;
 		allowed = ir_raw_get_allowed_protocols();
-	} else
+	} else {
+		mutex_unlock(&dev->lock);
 		return -ENODEV;
+	}
 
 	IR_dprintk(1, "allowed - 0x%llx, enabled - 0x%llx\n",
 		   (long long)allowed,