vhost: fix device leak on connection add failure

vhost: fix device leak on connection add failure

Need to destroy allocated device if application fails to
add new connection or we have fdset failure.

Fixes: acbff5c67ea7 ("vhost: fix crash when exceeding file descriptors")
Fixes: efba12a78ddf ("vhost: add user callbacks for socket open/close")
Cc: stable@dpdk.org
Reported-by: David Marchand <david.marchand@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Reviewed-by: David Marchand <david.marchand@redhat.com>
Reviewed-by: Jens Freimann <jfreimann@redhat.com>
Reviewed-by: Tiwei Bie <tiwei.bie@intel.com>