ASoC: stm32: dfsdm: fix debugfs warnings on entry creation

[ Upstream commit c47255b61129857b74b0d86eaf59335348be05e0 ]

Register platform component with a prefix, to avoid warnings
on debugfs entries creation, due to component name
redundancy.

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>