drm/i915/hdmi: use native encoder mode_set callback

Again drop the intel_ prefix from the intel_crtc local variable to
save a bit of space. But here I didn't switch the upcast macros to
intel_encoder since all our infoframe interfaces still use
drm_encoder. That needs to be changed first.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>