drm/amd/display: fix missing az disable in reset backend

Optimization in reset backend skips disable stream if it is
already done in dc_stream_set_dpms. However that path does
not disable az in order to prevent audio from toggling
between internal and external displays. This still need to
be done.

Signed-off-by: Eric Yang <Eric.Yang2@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>