drm/i915: Use IS_HSW_ULT() in a HSW specific code path

No need to add the BDW pci ULT/ULX checks inside a if (IS_HASWELL(dev))
code path.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>