dts: dragonboard820c: use correct bindings for clocks

Don't use hardcoded clock IDs, use the IDs from the dt-bindings to be
compatible with upstream.

Taken from kernel tag v6.7

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>