intel_th: fix device leak on output open()

Make sure to drop the reference taken when looking up the th device
during output device open() on errors and on close().

Note that a recent commit fixed the leak in a couple of open() error
paths but not all of them, and the reference is still leaking on
successful open().

Fixes: 39f4034693b7 ("intel_th: Add driver infrastructure for Intel(R) Trace Hub devices")
Fixes: 6d5925b667e4 ("intel_th: Fix error handling in intel_th_output_open")
Cc: [e-mail] # 4.4: 6d5925b667e4
Cc: Alexander Shishkin <[e-mail]>
Cc: Ma Ke <[e-mail]>
Signed-off-by: Johan Hovold <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/hwtracing/intel_th/core.c

···
 	int err;
 
 	dev = bus_find_device_by_devt(&intel_th_bus, inode->i_rdev);
-	if (!dev || !dev->driver) {
+	if (!dev)
+		return -ENODEV;
+
+	if (!dev->driver) {
 		err = -ENODEV;
-		goto out_no_device;
+		goto out_put_device;
 	}
 
 	thdrv = to_intel_th_driver(dev->driver);
···
 
 out_put_device:
 	put_device(dev);
-out_no_device:
+
 	return err;
+}
+
+static int intel_th_output_release(struct inode *inode, struct file *file)
+{
+	struct intel_th_device *thdev = file->private_data;
+
+	put_device(&thdev->dev);
+
+	return 0;
 }
 
 static const struct file_operations intel_th_output_fops = {
 	.open	= intel_th_output_open,
+	.release = intel_th_output_release,
 	.llseek	= noop_llseek,
 };