drm/i915: don't call dpms funcs after set_mode

... because our current set_mode implementation doesn't bother to adjust
for the dpms state, we just forcefully update it. So stop pretending that
we're better than we are and rip out this extranous call.

Note that this totally confuses userspace, because the exposed connector
property isn't actually updated ...

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>