drm/i915: remove unused variables from ironlake_crtc_mode_set

The last patches moved a lot of code from ironlake_crtc_mode_set to
sub-functions, so these variables became useless. You could get
warnings by enabling -Wunused-but-set-variable.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>