rtc: rx6110: Constify struct regmap_config

'regmap_spi_config' and 'regmap_i2c_config' are not modified in this diver
and are only used as a const struct regmap_config.

Constifying these structures moves some data to a read-only section, so
increase overall security.

On a x86_64, with allmodconfig:
Before:
   text	   data	    bss	    dec	    hex	filename
   8896	   1554	     32	  10482	   28f2	drivers/rtc/rtc-rx6110.o

After:
   text	   data	    bss	    dec	    hex	filename
   9536	    914	     32	  10482	   28f2	drivers/rtc/rtc-rx6110.o
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/833a7f612c0de9dcb1179a0b75b189c237a335ac.1714862560.git.christophe.jaillet@wanadoo.frSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-rx6110.c

@@ -330,7 +330,7 @@ static int rx6110_probe(struct rx6110_data *rx6110, struct device *dev)
 }
 
 #if IS_ENABLED(CONFIG_SPI_MASTER)
-static struct regmap_config regmap_spi_config = {
+static const struct regmap_config regmap_spi_config = {
 	.reg_bits = 8,
 	.val_bits = 8,
 	.max_register = RX6110_REG_IRQ,
@@ -410,7 +410,7 @@ static void rx6110_spi_unregister(void)
 #endif /* CONFIG_SPI_MASTER */
 
 #if IS_ENABLED(CONFIG_I2C)
-static struct regmap_config regmap_i2c_config = {
+static const struct regmap_config regmap_i2c_config = {
 	.reg_bits = 8,
 	.val_bits = 8,
 	.max_register = RX6110_REG_IRQ,