drm/i915: Fix cdclk bypass freq readout for tgl/bxt/glk

On tgl/bxt/glk the cdclk bypass frequency depends on the PLL
reference clock. So let's read out the ref clock before we
try to compute the bypass clock.

Cc: Matt Roper <matthew.d.roper@intel.com>
Fixes: 71dc367e ("drm/i915: Consolidate bxt/cnl/icl cdclk readout")
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NMatt Roper <matthew.d.roper@intel.com>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190911133129.27466-1-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/display/intel_cdclk.c

@@ -1351,6 +1351,8 @@ static void bxt_get_cdclk(struct drm_i915_private *dev_priv,
 	u32 divider;
 	int div;
 
+	bxt_de_pll_readout(dev_priv, cdclk_state);
+
 	if (INTEL_GEN(dev_priv) >= 12)
 		cdclk_state->bypass = cdclk_state->ref / 2;
 	else if (INTEL_GEN(dev_priv) >= 11)
@@ -1358,7 +1360,6 @@ static void bxt_get_cdclk(struct drm_i915_private *dev_priv,
 	else
 		cdclk_state->bypass = cdclk_state->ref;
 
-	bxt_de_pll_readout(dev_priv, cdclk_state);
 	if (cdclk_state->vco == 0) {
 		cdclk_state->cdclk = cdclk_state->bypass;
 		goto out;