drm/i915: convert force_wake_get to func pointer in the gpu reset code

This was forgotten in the original multi-threaded forcewake
conversion:

commit 8d715f00
Author: Keith Packard <keithp at keithp.com>
Date:   Fri Nov 18 20:39:01 2011 -0800

    drm/i915: add multi-threaded forcewake support

Signed-Off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Keith Packard <keithp@keithp.com>

drivers/gpu/drm/i915/i915_drv.c

@@ -645,7 +645,7 @@ int i915_reset(struct drm_device *dev, u8 flags)
 		ret = gen6_do_reset(dev, flags);
 		/* If reset with a user forcewake, try to restore */
 		if (atomic_read(&dev_priv->forcewake_count))
-			__gen6_gt_force_wake_get(dev_priv);
+			dev_priv->display.force_wake_get(dev_priv);
 		break;
 	case 5:
 		ret = ironlake_do_reset(dev, flags);