drm/tegra: Make tegra_drm_driver static

There is no need to access it from other files now that the driver has
been decoupled from host1x.

Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/tegra/drm.c

@@ -573,7 +573,7 @@ static void tegra_debugfs_cleanup(struct drm_minor *minor)
 }
 #endif
 
-struct drm_driver tegra_drm_driver = {
+static struct drm_driver tegra_drm_driver = {
 	.driver_features = DRIVER_MODESET | DRIVER_GEM,
 	.load = tegra_drm_load,
 	.unload = tegra_drm_unload,