mfd: let asic3 use mem resource instead of bus_shift

The bus_shift parameter in platform_data is not needed
as we can tell the driver with the IOMEM_RESOURCE whether
the ASIC is located on a 16bit or 32bit memory bus.

The htc-egpio driver uses a more descriptive bus_width parameter,
but for drivers where the register map size fixed, we don't even
need this.

Signed-off-by: Philipp Zabel <philipp.zabel@gmail.com>
Signed-off-by: Samuel Ortiz <sameo@openedhand.com>