ASoC: stm32: sai: fix iec958 controls indexation

[ Upstream commit 5f8a1000c3e630c3ac06f1d664eeaa755bce8823 ]

Allow indexation of sai iec958 controls according
to device id.

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>