drm/i915: Fix SRC_COPY width on 830/845g

One small change I forgot to make in

commit c4d69da1
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Mon Sep 8 14:25:41 2014 +0100

    drm/i915: Evict CS TLBs between batches

was to update the copy width for the compact BLT copy instruction.

Reported-by: Thomas Richter <thor@math.tu-berlin.de>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Thomas Richter <thor@math.tu-berlin.de>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: stable@vger.kernel.org
Tested-by: Thomas Richter <thor@math.tu-berlin.de>
Acked-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>