IB/iser: Use correct dma direction when unmapping SGs

commit c6c95ef4cec680f7a10aa425a9970744b35b6489 upstream.

We always unmap SGs with the same direction instead of unmapping
with the direction the mapping was done, fix that.

Fixes: 9a8b08fa ("IB/iser: Generalize iser_unmap_task_data and [...]")
Signed-off-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>