drm/i915: Remove set but unused 'gt_perf_status'

	struct drm_i915_private *dev_priv = dev->dev_private;

	struct intel_engine_cs *ring;

	u32 rp_state_cap;

	u32 gt_perf_status;

	u32 rc6vids, pcu_mbox = 0, rc6_mask = 0;

	u32 gtfifodbg;

	int rc6_mode;

	gen6_gt_force_wake_get(dev_priv, FORCEWAKE_ALL);

	rp_state_cap = I915_READ(GEN6_RP_STATE_CAP);

	gt_perf_status = I915_READ(GEN6_GT_PERF_STATUS);

	parse_rp_state_cap(dev_priv, rp_state_cap);