Add callbacks for setting and getting the sample rate. The callbacks are
optional if all Clock Source entities support only one sample rate.
This commit results in working High-Speed operation with Windows UAC2
driver when the Clock Source is host-programmable. Windows UAC2 driver
won't work if setting sample rate fails even if Clock Source supports
only one sample rate.
Signed-off-by: Tomasz Moń <tomasz.mon@nordicsemi.no>
4c6b1e5a65