power: supply: core: mark attribute arrays as ro_after_init

The attribute arrays are only modified during the __init phase.
To protect them against intentional or accidental modification,
mark them as __ro_after_init.

To make sure no modifications are introduced, also mark the return
values of the accessors as const.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/r/20241005-power-supply-cleanups-v1-3-45303b2d0a4d@weissschuh.net


Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>