drm/msm/dsi: fix direct caller of msm_gem_free_object()

This should be using drm_gem_object_put().  Also since this is done only
in driver unload path, we don't need to synchronize setting tx_gem_obj
to NULL, so juse use the _unlocked() variant.
Signed-off-by: Rob Clark <robdclark@gmail.com>

drivers/gpu/drm/msm/dsi/dsi_host.c

@@ -1063,10 +1063,8 @@ static void dsi_tx_buf_free(struct msm_dsi_host *msm_host)
 
 	if (msm_host->tx_gem_obj) {
 		msm_gem_put_iova(msm_host->tx_gem_obj, 0);
-		mutex_lock(&dev->struct_mutex);
-		msm_gem_free_object(msm_host->tx_gem_obj);
+		drm_gem_object_put_unlocked(msm_host->tx_gem_obj);
 		msm_host->tx_gem_obj = NULL;
-		mutex_unlock(&dev->struct_mutex);
 	}
 
 	if (msm_host->tx_buf)

drivers/gpu/drm/msm/msm_gem.c

@@ -798,6 +798,7 @@ void msm_gem_describe_objects(struct list_head *list, struct seq_file *m)
 }
 #endif
 
+/* don't call directly!  Use drm_gem_object_put() and friends */
 void msm_gem_free_object(struct drm_gem_object *obj)
 {
 	struct drm_device *dev = obj->dev;