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 <[e-mail]>
Link: https://lore.kernel.org/r/833a7f612c[e-mail]
Signed-off-by: Alexandre Belloni <[e-mail]>

drivers/rtc/rtc-rx6110.c

···
 }
 
 #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,
···
 #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,