drm: Move authmagic cleanup into drm_master_release

It's related, and soon authmagic will also use the master_mutex.

There is an ever-so-slightly semantic change here:
- authmagic will only be cleaned up for primary_client drm_minors. But
  it's impossible to create authmagic on render/control nodes, so this
  is fine.
- The cleanup is moved down a bit in the release processing. Doesn't
  matter at all since authmagic is purely internal logic used by the
  core ioctl access checks, and when we're in a file's release
  callback no one can do ioctls any more.

v2: Rebased.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> (v1)
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1466148814-8194-3-git-send-email-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_auth.c

@@ -248,6 +248,11 @@ void drm_master_release(struct drm_file *file_priv)
 	struct drm_device *dev = file_priv->minor->dev;
 	struct drm_master *master = file_priv->master;
 
+	mutex_lock(&dev->struct_mutex);
+	if (file_priv->magic)
+		idr_remove(&file_priv->master->magic_map, file_priv->magic);
+	mutex_unlock(&dev->struct_mutex);
+
 	mutex_lock(&dev->master_mutex);
 	if (!file_priv->is_master)
 		goto out;

drivers/gpu/drm/drm_fops.c

@@ -376,11 +376,6 @@ int drm_release(struct inode *inode, struct file *filp)
 	list_del(&file_priv->lhead);
 	mutex_unlock(&dev->filelist_mutex);
 
-	mutex_lock(&dev->struct_mutex);
-	if (file_priv->magic)
-		idr_remove(&file_priv->master->magic_map, file_priv->magic);
-	mutex_unlock(&dev->struct_mutex);
-
 	if (dev->driver->preclose)
 		dev->driver->preclose(dev, file_priv);