powerpc: fsl: 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>
[mpe: Add required include of of_address.h]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230609183151.1766261-1-robh@kernel.org