drm/amd/display: Unassign does_plane_fit_in_mall function from dcn3.2

[Why]
The hwss function does_plane_fit_in_mall not applicable to dcn3.2 asics.
Using it with dcn3.2 can result in undefined behaviour.

[How]
Assign the function pointer to NULL.

Reviewed-by: Alvin Lee <Alvin.Lee2@amd.com>
Acked-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: George Shen <george.shen@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>