drm/amdgpu: hide another #warning

An earlier patch of mine disabled some #warning statements
that get in the way of build testing, but then another
instance was added around the same time.

Remove that as well.

Fixes: b5203d16 ("drm/amd/amdgpu: hide #warning for missing DC config")
Fixes: e1c14c43 ("drm/amdgpu: Enable DC on Renoir")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>