drm: rcar-du: dsi: Fix VCLKSET write

rcar_mipi_dsi_startup() writes correct values to VCLKSET, but as it uses
or-operation to add the new values to the current value in the register,
it should first make sure the fields are cleared.

Do this by using rcar_mipi_dsi_write() to write the VCLKSET register
with a variable that has all the unused bits zeroed.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>

drivers/gpu/drm/rcar-du/rcar_mipi_dsi.c

@@ -415,7 +415,7 @@ static int rcar_mipi_dsi_startup(struct rcar_mipi_dsi *dsi,
 
 	/* Enable DOT clock */
 	vclkset = VCLKSET_CKEN;
-	rcar_mipi_dsi_set(dsi, VCLKSET, vclkset);
+	rcar_mipi_dsi_write(dsi, VCLKSET, vclkset);
 
 	if (dsi_format == 24)
 		vclkset |= VCLKSET_BPP_24;
@@ -430,7 +430,7 @@ static int rcar_mipi_dsi_startup(struct rcar_mipi_dsi *dsi,
 	vclkset |= VCLKSET_COLOR_RGB | VCLKSET_DIV(setup_info.div)
 		|  VCLKSET_LANE(dsi->lanes - 1);
 
-	rcar_mipi_dsi_set(dsi, VCLKSET, vclkset);
+	rcar_mipi_dsi_write(dsi, VCLKSET, vclkset);
 
 	/* After setting VCLKSET register, enable VCLKEN */
 	rcar_mipi_dsi_set(dsi, VCLKEN, VCLKEN_CKEN);