drm/i915: use the correct force_wake function at the PC8 code

When I submitted the first patch adding these force wake functions,
Chris Wilson observed that I was using the wrong functions, so I sent
a second version of the patch to correct this problem. The problem is
that v1 was merged instead of v2.

I was able to notice the problem when running the
debugfs-forcewake-user subtest of pm_pc8 from intel-gpu-tools.

Cc: stable@vger.kernel.org
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -6402,7 +6402,7 @@ static void hsw_restore_lcpll(struct drm_i915_private *dev_priv)
 
 	/* Make sure we're not on PC8 state before disabling PC8, otherwise
 	 * we'll hang the machine! */
-	dev_priv->uncore.funcs.force_wake_get(dev_priv);
+	gen6_gt_force_wake_get(dev_priv);
 
 	if (val & LCPLL_POWER_DOWN_ALLOW) {
 		val &= ~LCPLL_POWER_DOWN_ALLOW;
@@ -6436,7 +6436,7 @@ static void hsw_restore_lcpll(struct drm_i915_private *dev_priv)
 			DRM_ERROR("Switching back to LCPLL failed\n");
 	}
 
-	dev_priv->uncore.funcs.force_wake_put(dev_priv);
+	gen6_gt_force_wake_put(dev_priv);
 }
 
 void hsw_enable_pc8_work(struct work_struct *__work)