IB/iser: Modify struct iser_mem_reg members

No need to keep lkey, va, len variables, we can keep
them as struct ib_sge. This will help when we change the
memory registration logic.

This patch does not change any functionality.

Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Adir Lev <adirl@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

diff --cc drivers/infiniband/ulp/iser/iscsi_iser.h
Simple merge

diff --cc drivers/infiniband/ulp/iser/iser_initiator.c
Simple merge

diff --cc drivers/infiniband/ulp/iser/iser_memory.c
Simple merge