drm/amdgpu: fix error handling in amdgpu_bo_list_create

We need to drop normal and userptr BOs separately.

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>