We need to reset this or otherwise run into list corruption later on.

Fixes: e44a0fe6 ("drm/amdgpu: rework reserved VMID handling")
Signed-off-by: NChristian König <christian.koenig@amd.com>
Reviewed-by: NAlex Deucher <alexander.deucher@amd.com>
Tested-by: NCandice Li <candice.li@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>