drivers/counter nrfx: Fix with DT instance not matching device instance

478530ec0aa1fe5f481786c25d50f7a081b22208 introduced a bug
where if the DT index while iterating its DT structure
initialization does not match the actual peripheral instance,
or if the device instance string is not just a simple integer,
but a more complex string like "00", or "02", either
the wrong peripheral address would be used, or the file
would failt to compile.

Let's fix this by reverting that change, and instead, for
simulation converting the hardcoded DT/real HW address
to the valid addr for simulation on the fly.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>