drm/amd/display: dont set otg offset

move the update of otg instance outside of hw programming logic,
since this is sw state, it should always be updated and should
never be optimized away.

Signed-off-by: Jun Lei <Jun.Lei@amd.com>
Reviewed-by: Eric Yang <eric.yang2@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>