drm/amdgpu/smu10: fix smu10_get_clock_by_type_with_voltage

Cull out 0 clocks to avoid a warning in DC.

Bug: https://gitlab.freedesktop.org/drm/amd/issues/963
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>