macintosh: Use of_address_to_resource()

Replace open coded reading of "reg" and of_translate_address() calls with
single call to of_address_to_resource().

Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230319163226.226583-1-robh@kernel.org