net: mvneta: Fix err code path of probe

[ Upstream commit d484e06e ]

Fix below issues in err code path of probe:
1. we don't need to unregister_netdev() because the netdev isn't
registered.
2. when register_netdev() fails, we also need to destroy bm pool for
HWBM case.

Fixes: dc35a10f ("net: mvneta: bm: add support for hardware buffer management")
Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>