drm/tegra: gem: Remove redundant drm_gem_free_mmap_offset()

The drm_gem_object_release() function already performs this cleanup, so
there is no reason to do it explicitly.
Signed-off-by: NThierry Reding <treding@nvidia.com>

drivers/gpu/drm/tegra/gem.c

@@ -247,9 +247,7 @@ void tegra_bo_free_object(struct drm_gem_object *gem)
 		tegra_bo_destroy(gem->dev, bo);
 	}
 
-	drm_gem_free_mmap_offset(gem);
 	drm_gem_object_release(gem);
-
 	kfree(bo);
 }