ASoC: stm32: dfsdm: manage multiple prepare

[ Upstream commit 19441e35a43b616ea6afad91ed0d9e77268d8f6a ]

The DFSDM must be stopped when a new setting is applied.
restart systematically DFSDM on multiple prepare calls,
to apply changes.

Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>