drm/amd/display: Persist stream refcount through restore

drm/amd/display: Persist stream refcount through restore

[Why & How]
Overwriting the refcount on stream restore can lead to double-free errors
or memory leaks if an unbalanced number of retains and releases occurs
between a backup and restore.

Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Signed-off-by: Joshua Aberback <joshua.aberback@amd.com>
Signed-off-by: Ray Wu <ray.wu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>