drm/amdgpu: remove vm sanity check from amdgpu_vm_make_compute

Since we allow kfd and graphic operate on same GPU VM to have interoperation
between them GPU VM may have been used by graphic vm operations before kfd turns
a GPU VM into a compute VM. Remove vm clean checking at amdgpu_vm_make_compute.

Signed-off-by: Xiaogang Chen <xiaogang.chen@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>