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 <[e-mail]>
Signed-off-by: Thierry Reding <[e-mail]>

drivers/gpu/drm/tegra/hub.h

···
 	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);