mfd: syscon: Use regmap max_register_is_0 as needed

syscon has always set the optional max_register configuration of
regmap to ensure the correct checks are in place. However, a recent
commit 0ec74ad3 ("regmap: rework ->max_register handling")
introduced explicit configuration in regmap framework for register
maps that is exactly 1 register, when max_register is pointing to a
valid register 0. This commit solved a previous limitation of regmap
framework.

Update syscon driver to consistent in regmap configuration for
all sizes of syscons by using this new capability by setting
max_register_is_0, when the max_register is valid and 0.

Signed-off-by: Nishanth Menon <nm@ti.com>
Link: https://lore.kernel.org/r/20240903184710.1552067-1-nm@ti.com


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