drm/i915: Drop uncore spinlock for reading debugfs forcewake counters

The set of available structs is not protected by the spinlock, and for
the single read we can use READ_ONCE instead.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170323101944.21627-7-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_debugfs.c

@@ -1459,17 +1459,14 @@ static int ironlake_drpc_info(struct seq_file *m)
 
 static int i915_forcewake_domains(struct seq_file *m, void *data)
 {
-	struct drm_i915_private *dev_priv = node_to_i915(m->private);
+	struct drm_i915_private *i915 = node_to_i915(m->private);
 	struct intel_uncore_forcewake_domain *fw_domain;
 	unsigned int tmp;
 
-	spin_lock_irq(&dev_priv->uncore.lock);
-	for_each_fw_domain(fw_domain, dev_priv, tmp) {
+	for_each_fw_domain(fw_domain, i915, tmp)
 		seq_printf(m, "%s.wake_count = %u\n",
 			   intel_uncore_forcewake_domain_to_str(fw_domain->id),
-			   fw_domain->wake_count);
-	}
-	spin_unlock_irq(&dev_priv->uncore.lock);
+			   READ_ONCE(fw_domain->wake_count));
 
 	return 0;
 }