drm/i915/bxt: PORT_PLL_REF_SEL bit should be set for all BXT variations

This patch is to correct one thing in this commit:

commit 25a5670
Author: Dongwon Kim <dongwon.kim@intel.com>
Date:   Wed Mar 16 18:06:13 2016 -0700

    drm/i915/bxt: Reversed polarity of PORT_PLL_REF_SEL bit

This reversed bit polarity is actually common
for all BXT and APL SoCs. Therefore, revision checking
in the original commit should be removed to make
the bit set regardless of revision ID of GFX block.

Signed-off-by: Dongwon Kim <dongwon.kim@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1460673463-14453-1-git-send-email-dongwon.kim@intel.com

drivers/gpu/drm/i915/intel_dpll_mgr.c

@@ -1295,17 +1295,9 @@ static void bxt_ddi_pll_enable(struct drm_i915_private *dev_priv,
 	uint32_t temp;
 	enum port port = (enum port)pll->id;	/* 1:1 port->PLL mapping */
 
-	temp = I915_READ(BXT_PORT_PLL_ENABLE(port));
-	/*
-	 * Definition of each bit polarity has been changed
-	 * after A1 stepping
-	 */
-	if (IS_BXT_REVID(dev_priv, 0, BXT_REVID_A1))
-		temp &= ~PORT_PLL_REF_SEL;
-	else
-		temp |= PORT_PLL_REF_SEL;
-
 	/* Non-SSC reference */
+	temp = I915_READ(BXT_PORT_PLL_ENABLE(port));
+	temp |= PORT_PLL_REF_SEL;
 	I915_WRITE(BXT_PORT_PLL_ENABLE(port), temp);
 
 	/* Disable 10 bit clock */