bonding: don't use bond_next_slave() in bond_info_seq_next()

We don't need the circular loop there and it's the only current user of
bond_next_slave() - so just use the standard bond_for_each_slave().

CC: Jay Vosburgh <fubar@us.ibm.com>
CC: Andy Gospodarek <andy@greyhouse.net>
Signed-off-by: Veaceslav Falico <vfalico@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>