tipc: fix a double free in tipc_enable_bearer()

bearer_disable() already calls kfree_rcu() to free struct tipc_bearer,
we don't need to call kfree() again.

Fixes: cb30a633 ("tipc: refactor function tipc_enable_bearer()")
Reported-by:  <syzbot+b981acf1fb240c0c128b@syzkaller.appspotmail.com>
Cc: Ying Xue <ying.xue@windriver.com>
Cc: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>