drm/mediatek: dsi: Fix scrolling of panel with small hfp or hbp

BugLink: https://bugs.launchpad.net/bugs/1896795

[ Upstream commit 35bf948 ]

horizontal_backporch_byte should be hbp * bpp - hbp extra bytes.
So remove the wrong subtraction 10.

Fixes: 7a5bc4e ("drm/mediatek: change the dsi phytiming calculate method")
Signed-off-by: Jitao Shi <jitao.shi@mediatek.com>
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>

drivers/gpu/drm/mediatek/mtk_dsi.c

@@ -470,14 +470,13 @@ static void mtk_dsi_config_vdo_timing(struct mtk_dsi *dsi)
 	horizontal_sync_active_byte = (vm->hsync_len * dsi_tmp_buf_bpp - 10);
 
 	if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO_SYNC_PULSE)
-		horizontal_backporch_byte =
-			(vm->hback_porch * dsi_tmp_buf_bpp - 10);
+		horizontal_backporch_byte = vm->hback_porch * dsi_tmp_buf_bpp;
 	else
-		horizontal_backporch_byte = ((vm->hback_porch + vm->hsync_len) *
-			dsi_tmp_buf_bpp - 10);
+		horizontal_backporch_byte = (vm->hback_porch + vm->hsync_len) *
+					    dsi_tmp_buf_bpp;
 
 	data_phy_cycles = timing->lpx + timing->da_hs_prepare +
-			  timing->da_hs_zero + timing->da_hs_exit + 3;
+			  timing->da_hs_zero + timing->da_hs_exit;
 
 	if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO_BURST) {
 		if ((vm->hfront_porch + vm->hback_porch) * dsi_tmp_buf_bpp >