bnx2: Always enable MSI-X on 5709.

Minor change to use MSI-X even if there is only one CPU.  This allows
the CNIC driver to always have a dedicated MSI-X vector to handle
iSCSI events, instead of sharing the MSI vector.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>