be2net: fix return status of some ethtool methods

ethtool expects a -ve status value to be returned when a driver method
encounters an error. The driver was directly passing the
error status returned by FW (a positive value) to ethtool.
This patch fixes this by returning -EIO status in cases where FW returns
an error.
Signed-off-by: Kalesh AP <kalesh.purayil@emulex.com>
Signed-off-by: Sathya Perla <sathya.perla@emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>