drm/i915/vlv: Fix port B PLL opamp initialization

The current code looks like a typo, the specification calls for setting
bits 31:24 to 0x8C, while preserving bits 23:0. Fix things accordingly.

I'm not aware of the typo causing a real problem, so the fix is only for
consistency.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NImre Deak <imre.deak@intel.com>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1494408113-379-1-git-send-email-imre.deak@intel.com

drivers/gpu/drm/i915/intel_display.c

@@ -6369,8 +6369,8 @@ static void vlv_pllb_recal_opamp(struct drm_i915_private *dev_priv, enum pipe
 	vlv_dpio_write(dev_priv, pipe, VLV_PLL_DW9(1), reg_val);
 
 	reg_val = vlv_dpio_read(dev_priv, pipe, VLV_REF_DW13);
-	reg_val &= 0x8cffffff;
-	reg_val = 0x8c000000;
+	reg_val &= 0x00ffffff;
+	reg_val |= 0x8c000000;
 	vlv_dpio_write(dev_priv, pipe, VLV_REF_DW13, reg_val);
 
 	reg_val = vlv_dpio_read(dev_priv, pipe, VLV_PLL_DW9(1));