w1: ds1wm: fix register offset (bus shift) calculation

Replace incorrect register offsett calculation by
direct configuration of bus_shift in mfd-cell.

Indirect definition of address-shift by resource size
was unobvious and was wrong (should have used a binary log).

Signed-off-by: Johannes Poehlmann <johannes.poehlmann@izt-labs.de>
Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>