bus: sunxi-rsb: Constify struct regmap_bus

`regmap_sunxi_rsb` is not modified and can be declared as const to
move its data to a read-only section.
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Link: https://lore.kernel.org/r/20240705-sunxi-rsb-bus-const-regmap_bus-v1-1-129094960ce9@gmail.comSigned-off-by: Chen-Yu Tsai <wens@csie.org>

drivers/bus/sunxi-rsb.c

@@ -457,7 +457,7 @@ static void regmap_sunxi_rsb_free_ctx(void *context)
 	kfree(ctx);
 }
 
-static struct regmap_bus regmap_sunxi_rsb = {
+static const struct regmap_bus regmap_sunxi_rsb = {
 	.reg_write = regmap_sunxi_rsb_reg_write,
 	.reg_read = regmap_sunxi_rsb_reg_read,
 	.free_context = regmap_sunxi_rsb_free_ctx,