drm/display/dp_mst: Correct the kref of port.

[why & how]
We still need to refer to port while removing payload at commit_tail.
we should keep the kref till then to release.

Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/2171


Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Fixes: 4d07b0bc ("drm/display/dp_mst: Move all payload info into the atomic state")
Cc: stable@vger.kernel.org # 6.1
Acked-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Tested-by: Didier Raboud <odyx@debian.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>