ASoC: fsl_spdif: Use clk_set_rate() for spdif root clock only

The clock mux for the Freescale S/PDIF controller has eight clock sources
while most of them are from other moudles and even system clocks that do
not allow a rate-changing operation.

So we here only allow the clk_set_rate() and clk_round_rate() happened to
spdif root clock, the private clock for S/PDIF controller.

Signed-off-by: Nicolin Chen <Guangyu.Chen@freescale.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

sound/soc/fsl/fsl_spdif.h

@@ -157,6 +157,8 @@ enum spdif_gainsel {
 #define STC_TXCLK_DIV(x)		((((x) - 1) << STC_TXCLK_DIV_OFFSET) & STC_TXCLK_DIV_MASK)
 #define STC_TXCLK_SRC_MAX		8
 
+#define STC_TXCLK_SPDIF_ROOT		1
+
 /* SPDIF tx rate */
 enum spdif_txrate {
 	SPDIF_TXRATE_32000 = 0,