drm/i915: use PIPECONF_INTERLACE_MASK_HSW on lpt_enable_pch_transcoder

... instead of PIPECONF_INTERLACE_MASK.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
[danvet: applied the change by hand due to patch reorder.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>