Buffer length was assigned twice, and no reason to set va to
io_addr and then add the offset, just set va to io_addr + offset.

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>