drm/exynos: remove extra declaration of struct exynos_drm_manager

The struct is defined in the same file, declare it here is just
unnecessary.
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_encoder.h

@@ -14,8 +14,6 @@
 #ifndef _EXYNOS_DRM_ENCODER_H_
 #define _EXYNOS_DRM_ENCODER_H_
 
-struct exynos_drm_manager;
-
 void exynos_drm_encoder_setup(struct drm_device *dev);
 struct drm_encoder *exynos_drm_encoder_create(struct drm_device *dev,
 			struct exynos_drm_display *mgr,