drm/exynos: initialize the buf_num in vp_video_buffer

The buf_num in vp_video_buffer() should be 1 or 2, but it is not
initialized, and only set to 2 in NV12M or NV12MT cases.
So this patch initializes the buf_num with 1 as default.
Signed-off-by: NYoungJun Cho <yj44.cho@samsung.com>
Signed-off-by: NSeung-Woo Kim <sw0312.kim@samsung.com>
Signed-off-by: NKyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: NInki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_mixer.c

@@ -379,7 +379,7 @@ static void vp_video_buffer(struct mixer_context *ctx, int win)
 	unsigned long flags;
 	struct hdmi_win_data *win_data;
 	unsigned int x_ratio, y_ratio;
-	unsigned int buf_num;
+	unsigned int buf_num = 1;
 	dma_addr_t luma_addr[2], chroma_addr[2];
 	bool tiled_mode = false;
 	bool crcb_mode = false;