drm/tegra: Plug memory leak

Free the DRM device-private memory upon driver unload to make sure the
memory doesn't leak.

Signed-off-by: Thierry Reding <treding@nvidia.com>
diff --git a/drivers/gpu/drm/tegra/drm.c b/drivers/gpu/drm/tegra/drm.c
index 6c9df79..e549afe 100644
--- a/drivers/gpu/drm/tegra/drm.c
+++ b/drivers/gpu/drm/tegra/drm.c
@@ -118,6 +118,8 @@
 		drm_mm_takedown(&tegra->mm);
 	}
 
+	kfree(tegra);
+
 	return 0;
 }