drm/amd/display: Reformat dm_determine_update_type_for_commit

[Why]
The indenting for this function is a few levels too deep and can be
simplified a fair bit. This patch is in preparation for functional
changes that fix update type determination to occur less frequently
and more accurately.

[How]
Place checks early and exit/continue when possible. This isn't
a functional change.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: David Francis <David.Francis@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>