drm/i915: re-add locking around hw state readout

To silence locking complaints.  This was a rebase failure on my part in

commit fa9fa083
Author: Jesse Barnes <jbarnes@virtuousgeek.org>
Date:   Tue Feb 11 15:28:56 2014 -0800

    drm/i915: read out hw state earlier v2

Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>