drm/amd/display: Change initializer to single brace

[Why & How]
Change struct initializer from multiple brace to single brace.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Acked-by: Alan Liu <HaoPing.Liu@amd.com>
Signed-off-by: Aric Cyr <aric.cyr@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>