leds: is31fl319x: Constify struct regmap_config

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 <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/82a5cb26ff8af1865a790286bdbc3c4a2bd149f1.1714892598.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Lee Jones <lee@kernel.org>