mfd: core: Use of_property_read_reg() to parse "reg"

Use the recently added of_property_read_reg() helper to get the
untranslated "reg" address value.

Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230609183159.1766429-1-robh@kernel.org


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