ASoC: fsl_ssi: call _fsl_ssi_set_dai_fmt() just once in AC'97 mode

In AC'97 mode we configure and start SSI RX / TX on probe path via
a call to _fsl_ssi_set_dai_fmt() function.
We don't need to call this function again later and in fact don't want to
do it since this function temporarily sets STCR, SRCR and SCR to some
intermediate values.

Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
Acked-by: Nicolin Chen <nicoleotsuka@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>