drm/i915: Restore the invalid access without RPM warning

A long time ago we turned off the warning as it was too painful, we had
too much broken code. Turn it back on now as we are mostly clean and
need to prevent returning to such orangeness.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Imre Deak <imre.deak@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170302074157.21631-2-chris@chris-wilson.co.uk
Reviewed-by: Imre Deak <imre.deak@intel.com>

drivers/gpu/drm/i915/intel_drv.h

@@ -1739,10 +1739,8 @@ static inline void
 assert_rpm_wakelock_held(struct drm_i915_private *dev_priv)
 {
 	assert_rpm_device_not_suspended(dev_priv);
-	/* FIXME: Needs to be converted back to WARN_ONCE, but currently causes
-	 * too much noise. */
-	if (!atomic_read(&dev_priv->pm.wakeref_count))
-		DRM_DEBUG_DRIVER("RPM wakelock ref not held during HW access");
+	WARN_ONCE(!atomic_read(&dev_priv->pm.wakeref_count),
+		  "RPM wakelock ref not held during HW access");
 }
 
 /**