ASoC: fsl: fsl_spdif: Check for clk_prepare_enable() error

clk_prepare_enable() may fail, so we should better check its return value
and propagate it in the case of error.

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