ASoC: stm32: dfsdm: change rate limits

The DFSDM can support a larger rate range than currently
supported in driver.
Increase rate upper limit to 48kHz and allow all rates
in the range 8kHz to 48kHz.

Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
Link: https://lore.kernel.org/r/20201007153459.22155-2-olivier.moysan@st.com


Signed-off-by: Mark Brown <broonie@kernel.org>