ASoC: fsl_esai: Add freq check in set_dai_sysclk()

The freq parameter indicates the physical frequency of an actual
input clock or a desired frequency of an output clock for HCKT/R.
It should never be passed 0. This might cause Division-by-zero.

So this patch adds a check to fix it.

Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Mark Brown <broonie@kernel.org>