sh: dma-sysfs: Make dma_subsys const

Now that the driver core can properly handle constant struct bus_type,
move the dma_subsys variable to be a constant structure as well,
placing it into read-only memory which can not be modified at runtime.

Cc: Greg Kroah-Hartman <[e-mail]>
Suggested-by: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Ricardo B. Marliere <[e-mail]>
Reviewed-by: Geert Uytterhoeven <[e-mail]>
Reviewed-by: Greg Kroah-Hartman <[e-mail]>
Reviewed-by: John Paul Adrian Glaubitz <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: John Paul Adrian Glaubitz <[e-mail]>

arch/sh/drivers/dma/dma-sysfs.c

···
 #include <linux/string.h>
 #include <asm/dma.h>
 
-static struct bus_type dma_subsys = {
+static const struct bus_type dma_subsys = {
 	.name = "dma",
 	.dev_name = "dma",
 };