mfd: gateworks-gsc: Constify struct regmap_bus

`gsc_regmap_bus` 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/20240704-mfd-const-regmap_config-v2-22-0c8785b1331d@gmail.comSigned-off-by: Lee Jones <lee@kernel.org>

drivers/mfd/gateworks-gsc.c

@@ -160,7 +160,7 @@ static const struct of_device_id gsc_of_match[] = {
 };
 MODULE_DEVICE_TABLE(of, gsc_of_match);
 
-static struct regmap_bus gsc_regmap_bus = {
+static const struct regmap_bus gsc_regmap_bus = {
 	.reg_read = gsc_read,
 	.reg_write = gsc_write,
 };