RDMA/i40iw: Fix potential use after free

Release variable dst after logging dst->error to avoid possible use after
free.

Link: https://lore.kernel.org/r/1573022651-37171-1-git-send-email-bianpan2016@163.com


Signed-off-by: Pan Bian <bianpan2016@163.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>