net: dsa: qca8k: constify struct regmap_config

`qca8k_regmap_config` 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>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://patch.msgid.link/20240703-net-const-regmap-v1-1-ff4aeceda02c@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/qca/qca8k-8xxx.c

@@ -565,7 +565,7 @@ qca8k_regmap_update_bits(void *ctx, uint32_t reg, uint32_t mask, uint32_t write_
 	return qca8k_regmap_update_bits_mii(priv, reg, mask, write_val);
 }
 
-static struct regmap_config qca8k_regmap_config = {
+static const struct regmap_config qca8k_regmap_config = {
 	.reg_bits = 16,
 	.val_bits = 32,
 	.reg_stride = 4,