ASoC: sti: set iec958 channel status sampling freq

Previously, the iec958 channels status sampling freq was set only if not
already set. It means that it is not updated for next PCM sessions.
With this patch, we ensure the iec958 channels status sampling freq is set
to the runtime rate for each PCM session.

Signed-off-by: Moise Gergaud <moise.gergaud@st.com>
Acked-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Signed-off-by: Mark Brown <broonie@kernel.org>