RDS/IW: Remove page_shift variable from iwarp transport

The existing code treated page_shift as a variable, when in fact we
always want to have the fastreg page size be the same as the arch's
page size -- and it is, so this doesn't need to be a variable.

Signed-off-by: Andy Grover <andy.grover@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>