drm/i915: PSR: Remove wrong LINK_DISABLE.

This wrong logic and useless define came from first versions and
came along with all rework. Just now I notice how ugly, wrong and
useless this is.

val is already defined as 0 anyway and logic is completelly wrong
and useless. So let's starting the link_standby fix with this
cleaning.

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>