drm/tegra: Remove duplicate struct declaration

struct tegra_dc is declared at 13rd line.
The declaration here is unnecessary. Remove it.
Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/tegra/hub.h

@@ -72,7 +72,6 @@ to_tegra_display_hub_state(struct drm_private_state *priv)
 	return container_of(priv, struct tegra_display_hub_state, base);
 }
 
-struct tegra_dc;
 struct tegra_plane;
 
 int tegra_display_hub_prepare(struct tegra_display_hub *hub);