drm/i915: Don't accidentally increase the frequency in handling DOWN rps

If we receive a DOWN_TIMEOUT rps interrupt, we respond by reducing the
GPU clocks significantly. Before we do, double check that the frequency
we pick is actually a decrease.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170210150348.22146-2-chris@chris-wilson.co.ukReviewed-by: Radoslaw Szwichtenberg <radoslaw.szwichtenberg@intel.com>

drivers/gpu/drm/i915/i915_irq.c

@@ -1186,7 +1186,7 @@ static void gen6_pm_rps_work(struct work_struct *work)
 	} else if (pm_iir & GEN6_PM_RP_DOWN_TIMEOUT) {
 		if (dev_priv->rps.cur_freq > dev_priv->rps.efficient_freq)
 			new_delay = dev_priv->rps.efficient_freq;
-		else
+		else if (dev_priv->rps.cur_freq > dev_priv->rps.min_freq_softlimit)
 			new_delay = dev_priv->rps.min_freq_softlimit;
 		adj = 0;
 	} else if (pm_iir & GEN6_PM_RP_DOWN_THRESHOLD) {