RDMA/usnic: Fix memleak in find_free_vf_and_create_qp_grp

If usnic_ib_qp_grp_create() fails at the first call, dev_list
will not be freed on error, which leads to memleak.

Fixes: e3cf00d0

 ("IB/usnic: Add Cisco VIC low-level hardware driver")
Link: https://lore.kernel.org/r/20201226074248.2893-1-dinghao.liu@zju.edu.cn
Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>