drm/amd/display: fix some style issues

Fixes a few style issues:
- Only calculate the dto_params and dp_hpo_inst when dccg is present.
- Fix indentation
- Drop empty else block

Fixes: 7f7925e2

 ("drm/amd/display: Fix MST recognizes connected displays as one")
Cc: Muhammad Ahmed <ahmed.ahmed@amd.com>
Cc: Michel Dänzer <michel@daenzer.net>
Cc: Stylon Wang <stylon.wang@amd.com>
Reviewed-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>