drm/amd/display: Use local structs instead of struct pointers

Change struct pointers to creating structs on a stack.
Thats fixing a mistake in a previous patch introducing dm_pplib functions

Signed-off-by: Mikita Lipski <mikita.lipski@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>