[SPARC64]: Fix two bugs wrt. kernel 4MB TSB.

1) The TSB lookup was not using the correct hash mask.

2) It was not aligned on a boundary equal to it's size,
   which is required by the sun4v Hypervisor.

wasn't having it's return value checked, and that bug will be fixed up
as well in a subsequent changeset.

Signed-off-by: David S. Miller <davem@davemloft.net>