[POWERPC] pasemi: Another IOMMU bugfix for 64K PAGE_SIZE

More fallout from the switch from PAGE_SIZE based IOMMU to the native page
size for the driver. By pure luck it happened to work most of the time, since
we end up invalidating the wrong entries in the TLB.

Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>