drm/i915/hdmi: Remove redundant IS_VLV checks

Those functions are only used on vlv platforms, so no need to check.
Especially if we're not too consistent about it.

Reviewed-by: Naresh Kumar Kachhi <naresh.kumar.kachhi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>