qed: Zero-out the buffer paased to dcbx_query() API

qed_dcbx_query_params() implementation populate the values to input
buffer based on the dcbx mode and, the current negotiated state/params,
the caller of this API need to memset the buffer to zero.

Signed-off-by: Sudarsana Reddy Kalluru <Sudarsana.Kalluru@cavium.com>
Signed-off-by: Yuval Mintz <Yuval.Mintz@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>