drm/bridge: analogix-anx78xx: Fix drm_dp_link helper removal

drm_dp_link_rate_to_bw_code and ...bw_code_to_link_rate simply divide by
and multiply with 27000, respectively. Avoid an overflow in the u8 dpcd[0]
and the multiply+divide alltogether.

Signed-off-by: Torsten Duwe <duwe@lst.de>
Fixes: ff1e8fb ("drm/bridge: analogix-anx78xx: Avoid drm_dp_link helpers")
Cc: Thierry Reding <treding@nvidia.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Andrzej Hajda <a.hajda@samsung.com>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Cc: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
Cc: Jonas Karlman <jonas@kwiboo.se>
Cc: Jernej Skrabec <jernej.skrabec@siol.net>
Cc: <stable@vger.kernel.org> # v5.5+
Reviewed-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20200218155744.9675368BE1@verein.lst.de

drivers/gpu/drm/bridge/analogix/analogix-anx78xx.c

@@ -722,10 +722,9 @@ static int anx78xx_dp_link_training(struct anx78xx *anx78xx)
 	if (err)
 		return err;
 
-	dpcd[0] = drm_dp_max_link_rate(anx78xx->dpcd);
-	dpcd[0] = drm_dp_link_rate_to_bw_code(dpcd[0]);
 	err = regmap_write(anx78xx->map[I2C_IDX_TX_P0],
-			   SP_DP_MAIN_LINK_BW_SET_REG, dpcd[0]);
+			   SP_DP_MAIN_LINK_BW_SET_REG,
+			   anx78xx->dpcd[DP_MAX_LINK_RATE]);
 	if (err)
 		return err;