drm/amd/display: Fix dpstreamclk programming

drm/amd/display: Fix dpstreamclk programming

[WHY]
Currently programming incorrect hpo inst as well as selecting incorrect source

[HOW]
Use hpo inst instead of otg inst to select dpstreamclk inst

Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>