drm/tegra: plane: Make tegra_plane_get_overlap_index() static

This function is not used outside of the file and can be static.
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/tegra/plane.c

@@ -302,7 +302,7 @@ int tegra_plane_format_get_alpha(unsigned int opaque, unsigned int *alpha)
 	return -EINVAL;
 }
 
-unsigned int tegra_plane_get_overlap_index(struct tegra_plane *plane,
+static unsigned int tegra_plane_get_overlap_index(struct tegra_plane *plane,
 						  struct tegra_plane *other)
 {
 	unsigned int index = 0, i;