leds: is31fl319x: Constify struct regmap_config

'is31fl3190_regmap_config' and 'is31fl3196_regmap_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
13827 2002 32 15861 3df5 drivers/leds/leds-is31fl319x.o

After:
text data bss dec hex filename
14467 1370 32 15869 3dfd drivers/leds/leds-is31fl319x.o

Signed-off-by: Christophe JAILLET <[e-mail]>
Link: https://lore.kernel.org/r/82a5cb26ff[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

drivers/leds/leds-is31fl319x.c

···
 	{ IS31FL3190_PWM(2), 0x00 },
 };
 
-static struct regmap_config is31fl3190_regmap_config = {
+static const struct regmap_config is31fl3190_regmap_config = {
 	.reg_bits = 8,
 	.val_bits = 8,
 	.max_register = IS31FL3190_RESET,
···
 	{ IS31FL3196_PWM(8), 0x00 },
 };
 
-static struct regmap_config is31fl3196_regmap_config = {
+static const struct regmap_config is31fl3196_regmap_config = {
 	.reg_bits = 8,
 	.val_bits = 8,
 	.max_register = IS31FL3196_REG_CNT,