drm/i915: PSR HSW/BDW: Fix inverted logic at sink main_link_active bit.

We have only two possible states with so many names and combinations that
might be confusing.

1 - Main link active / enabled / stand by / on
2 - Main link disabled / off / full off

Let's start organizing it by fixing a inverted logic when setting the sink bit.

Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Durgadoss R <durgadoss.r@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>