net: encx24j600: constify struct regmap_bus/regmap_config

`regmap_encx24j600`, `phycfg` and `phymap_encx24j600` are not modified
and can be declared as const to move their data to a read-only section.
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Link: https://patch.msgid.link/20240703-net-const-regmap-v1-3-ff4aeceda02c@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/microchip/encx24j600-regmap.c

@@ -474,13 +474,13 @@ static struct regmap_config regcfg = {
 	.unlock = regmap_unlock_mutex,
 };
 
-static struct regmap_bus regmap_encx24j600 = {
+static const struct regmap_bus regmap_encx24j600 = {
 	.write = regmap_encx24j600_write,
 	.read = regmap_encx24j600_read,
 	.reg_update_bits = regmap_encx24j600_reg_update_bits,
 };
 
-static struct regmap_config phycfg = {
+static const struct regmap_config phycfg = {
 	.name = "phy",
 	.reg_bits = 8,
 	.val_bits = 16,
@@ -492,7 +492,7 @@ static struct regmap_config phycfg = {
 	.volatile_reg = encx24j600_phymap_volatile,
 };
 
-static struct regmap_bus phymap_encx24j600 = {
+static const struct regmap_bus phymap_encx24j600 = {
 	.reg_write = regmap_encx24j600_phy_reg_write,
 	.reg_read = regmap_encx24j600_phy_reg_read,
 };