drm/amd/display: Fix dmub timeout after fams2 enabled

Reset fams stream count upon stream removal, otherwise
fams2 state machine in dmub will get corrupted.

Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Signed-off-by: Jerry Zuo <jerry.zuo@amd.com>
Signed-off-by: Fangzhi Zuo <jerry.zuo@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>