qlcnic: fix inconsistent lock state

Spin_lock(rds_ring->lock) is not required while posting buffers
from qlcnic_open and freeing buffers from qlcnic_down.

Signed-off-by: Amit Kumar Salecha <amit.salecha@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>