ASoC: fsl_ssi: Redefine RX and TX macros

The RX and TX macros were defined implicitly and there was
a potential risk if someone changes their values.

Since they were defined to index the array ssi->regvals[2],
this patch moves these two macros to fsl_ssi.c, closer to
its owner ssi->regvals. And it also puts some comments here
to limit their value within [0, 1].
Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
Tested-by: Caleb Crome <caleb@crome.org>
Tested-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
Reviewed-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/fsl/fsl_ssi.c

@@ -56,6 +56,10 @@
 #include "fsl_ssi.h"
 #include "imx-pcm.h"
 
+/* Define RX and TX to index ssi->regvals array; Can be 0 or 1 only */
+#define RX 0
+#define TX 1
+
 /**
  * FSLSSI_I2S_FORMATS: audio formats supported by the SSI
  *

sound/soc/fsl/fsl_ssi.h

@@ -12,9 +12,6 @@
 #ifndef _MPC8610_I2S_H
 #define _MPC8610_I2S_H
 
-#define RX 0
-#define TX 1
-
 /* -- SSI Register Map -- */
 
 /* SSI Transmit Data Register 0 */