drm/i915: don't call ironlake_enable_pch_pll on lpt_pch_enable

This is just wrong. The lpt_program_iclkip should disable the PCH
pixel clocks (and yes, we plan to rename it later).

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