drm/sun4i: tcon: Fix tcon channel 1 backporch calculation

It seems like what's called a backporch in the datasheet is actually the
backporch plus the sync period. Fix that in our driver.
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

drivers/gpu/drm/sun4i/sun4i_tcon.c

@@ -269,7 +269,7 @@ void sun4i_tcon1_mode_set(struct sun4i_tcon *tcon,
 		     SUN4I_TCON1_BASIC2_Y(mode->crtc_vdisplay));
 
 	/* Set horizontal display timings */
-	bp = mode->crtc_htotal - mode->crtc_hsync_end;
+	bp = mode->crtc_htotal - mode->crtc_hsync_start;
 	DRM_DEBUG_DRIVER("Setting horizontal total %d, backporch %d\n",
 			 mode->htotal, bp);
 	regmap_write(tcon->regs, SUN4I_TCON1_BASIC3_REG,
@@ -277,7 +277,7 @@ void sun4i_tcon1_mode_set(struct sun4i_tcon *tcon,
 		     SUN4I_TCON1_BASIC3_H_BACKPORCH(bp));
 
 	/* Set vertical display timings */
-	bp = mode->crtc_vtotal - mode->crtc_vsync_end;
+	bp = mode->crtc_vtotal - mode->crtc_vsync_start;
 	DRM_DEBUG_DRIVER("Setting vertical total %d, backporch %d\n",
 			 mode->vtotal, bp);
 	regmap_write(tcon->regs, SUN4I_TCON1_BASIC4_REG,