drm/amd/display: Properly reuse completion structure

[Why]
Connecting displays to TBT3 docks often produces invalid
replies for DPIA AUX requests. It turns out the completion
structure was not re-initialized before reusing it, resulting
in immature wake up to completion.

[How]
Properly call reinit_completion() on reused completion structure.

Cc: stable@vger.kernel.org

Reviewed-by: Solomon Chiu <solomon.chiu@amd.com>
Acked-by: Alan Liu <HaoPing.Liu@amd.com>
Signed-off-by: Stylon Wang <stylon.wang@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>