be2net: fix error status for FW-download

For FW download ethtool cmd, if the user provides an FW-image incompatible
with the chip, return -EINVAL instead of -1.

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>