RDMA/cma: Delete useless kfree code

The parameter of kfree function is NULL, so kfree code is useless, delete
it.  Therefore, goto expression is no longer needed, so simplify
it. cma_dev_group is always pre-zero'd before reaching make_cma_ports, so
the NULL set to cma_dev_group->ports is unneeded too.

Link: https://lore.kernel.org/r/20201216080219.18184-1-zhengyongjun3@huawei.com


Signed-off-by: Zheng Yongjun <zhengyongjun3@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>