drm/i915: remove dead code in ironlake_crtc_mode_set

In

Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Wed Jun 5 13:34:23 2013 +0200

    drm/i915: consolidate pch pll enable sequence

I've removed all the code from this if block, but somehow forgotten to
kill the block itself.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>