drm/amdgpu: return EINVAL instead of ENOENT in the VM code

That we can't find a PD above the root is expected can only happen if
we try to update a larger range than actually managed by the VM.

Signed-off-by: Christian König <christian.koenig@amd.com>
Tested-by: Tom St Denis <tom.stdenis@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>