drm/i915: Sanity check cdclk in vlv_set_cdclk()

chv_set_cdclk() sanity checks that the cdclk frequency is one of the
legal values. Do the same in the VLV function.

Cc: Mika Kahola <mika.kahola@intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171024095216.1638-10-ville.syrjala@linux.intel.com
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/i915/intel_cdclk.c

@@ -520,6 +520,18 @@ static void vlv_set_cdclk(struct drm_i915_private *dev_priv,
 	int cdclk = cdclk_state->cdclk;
 	u32 val, cmd = cdclk_state->voltage_level;
 
+	switch (cdclk) {
+	case 400000:
+	case 333333:
+	case 320000:
+	case 266667:
+	case 200000:
+		break;
+	default:
+		MISSING_CASE(cdclk);
+		return;
+	}
+
 	/* There are cases where we can end up here with power domains
 	 * off and a CDCLK frequency other than the minimum, like when
 	 * issuing a modeset without actually changing any display after