mfd: tps65910: Constify struct regmap_irq_chip

`tps65910_irq_chip` and `tps65911_irq_chip` are not modified and can be
declared as const to move their data to a read-only section.

The pointer used to reference those structs has also been converted to
const.

Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Link: https://lore.kernel.org/r/20240704-mfd-const-regmap_config-v2-19-0c8785b1331d@gmail.com


Signed-off-by: Lee Jones <lee@kernel.org>