drm/exynos: remove to call mixer_wait_for_vblank

The reason waiting vblank is to be power gated and disabled clocks after
dma operation is completed. The dma operation is stopped already before
be power gated and clocks are disabled when mixer is disabled by commit
381be025("drm/exynos: stop mixer before gating clocks during
poweroff"). Don't need to wait vblank anymore.
Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_mixer.c

@@ -1010,7 +1010,6 @@ static void mixer_window_suspend(struct mixer_context *ctx)
 		plane->resume = plane->enabled;
 		mixer_win_disable(ctx->crtc, i);
 	}
-	mixer_wait_for_vblank(ctx->crtc);
 }
 
 static void mixer_window_resume(struct mixer_context *ctx)