svcrdma: Unregister the device if svc_rdma_accept() fails

To handle device removal, svc_rdma_accept() requests removal
notification for the underlying device when accepting a connection.
However svc_rdma_free() is not invoked if svc_rdma_accept() fails.
There needs to be a matching "unregister" in that case; otherwise
the device cannot be removed.

Fixes: c4de97f7 ("svcrdma: Handle device removal outside of the CM event handler")
Cc: stable@vger.kernel.org
Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>