ASoC: renesas: fsi: Constify struct fsi_stream_handler

'struct fsi_stream_handler' is not modified in this driver.

Constifying this structure moves some data to a read-only section, so
increases overall security, especially when the structure holds some
function pointers.

On a x86_64, with allmodconfig:
Before:
======
text data bss dec hex filename
51837 12312 64 64213 fad5 sound/soc/renesas/fsi.o

After:
=====
text data bss dec hex filename
52125 12024 64 64213 fad5 sound/soc/renesas/fsi.o

Signed-off-by: Christophe JAILLET <[e-mail]>
Acked-by: Kuninori Morimoto <[e-mail]>
Link: https://patch.msgid.link/88ca34df90[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

sound/soc/renesas/fsi.c

···
 	/*
 	 * these are initialized by fsi_handler_init()
 	 */
-	struct fsi_stream_handler *handler;
+	const struct fsi_stream_handler *handler;
 	struct fsi_priv		*priv;
 
 	/*
···
 	return 0;
 }
 
-static struct fsi_stream_handler fsi_pio_push_handler = {
+static const struct fsi_stream_handler fsi_pio_push_handler = {
 	.init		= fsi_pio_push_init,
 	.transfer	= fsi_pio_push,
 	.start_stop	= fsi_pio_start_stop,
 };
 
-static struct fsi_stream_handler fsi_pio_pop_handler = {
+static const struct fsi_stream_handler fsi_pio_pop_handler = {
 	.init		= fsi_pio_pop_init,
 	.transfer	= fsi_pio_pop,
 	.start_stop	= fsi_pio_start_stop,
···
 	return 0;
 }
 
-static struct fsi_stream_handler fsi_dma_push_handler = {
+static const struct fsi_stream_handler fsi_dma_push_handler = {
 	.init		= fsi_dma_init,
 	.probe		= fsi_dma_probe,
 	.transfer	= fsi_dma_transfer,