nvme-rdma: fix error code in nvme_rdma_setup_ctrl

In case that icdoff is not zero or mandatory keyed sgls are not
supported by the NVMe/RDMA target, we'll go to error flow but we'll
return 0 to the caller. Fix it by returning an appropriate error code.

Fixes: c66e2998 ("nvme-rdma: centralize controller setup sequence")
Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>