mfd: tps6594: Use volatile_table instead of volatile_reg

In regmap_config use volatile_table instead of volatile_reg. This change
makes it easier to add support for TPS65224 PMIC.

Signed-off-by: Bhargav Raviprakash <bhargav.r@ltts.com>
Acked-by: Julien Panis <jpanis@baylibre.com>
Link: https://lore.kernel.org/r/0109018f2f267f6e-3121fa42-4816-45f7-a96d-0d6b4678da5a-000000@ap-south-1.amazonses.com


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