ASoC: stm32: fix sai driver name initialisation

commit 17d3069ccf06970e2db3f7cbf4335f207524279e upstream.

This patch fixes the sai driver structure overwriting which results in
a cpu dai name equal NULL.

Fixes: 3e086edf ("ASoC: stm32: add SAI driver")

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>