drm/bridge: tc358768: Enable reference clock

The driver assumes that reference clock is always-enabled, but this is
hardware-dependent and not true for ASUS Transformer TF700T. Make driver
enable / disable the reference clock.

Tested-by: Andreas Westman Dorcsak <hedmoo@yahoo.com> # Asus TF700T
Tested-by: Maxim Schwalm <maxim.schwalm@gmail.com> #TF700T
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20211002233447.1105-2-digetx@gmail.com

drivers/gpu/drm/bridge/tc358768.c

@@ -237,6 +237,10 @@ static void tc358768_hw_enable(struct tc358768_priv *priv)
 	if (priv->enabled)
 		return;
 
+	ret = clk_prepare_enable(priv->refclk);
+	if (ret < 0)
+		dev_err(priv->dev, "error enabling refclk (%d)\n", ret);
+
 	ret = regulator_bulk_enable(ARRAY_SIZE(priv->supplies), priv->supplies);
 	if (ret < 0)
 		dev_err(priv->dev, "error enabling regulators (%d)\n", ret);
@@ -274,6 +278,8 @@ static void tc358768_hw_disable(struct tc358768_priv *priv)
 	if (ret < 0)
 		dev_err(priv->dev, "error disabling regulators (%d)\n", ret);
 
+	clk_disable_unprepare(priv->refclk);
+
 	priv->enabled = false;
 }