drm/amd/display: clean code-style issues in dcn30_set_mpc_shaper_3dlut

This function has many conditions and all code style issues (identation,
missing braces, etc.) make reading it really annoying.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Melissa Wen <mwen@igalia.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>