octeontx2-pf: Fix otx2_get_fecparam()

Static checkers complained about an off by one read overflow in
otx2_get_fecparam() and we applied two conflicting fixes for it.

Correct: b0aae0bd ("octeontx2: Fix condition.")
  Wrong: 93efb0c6 ("octeontx2-pf: Fix out-of-bounds read in otx2_get_fecparam()")

Revert the incorrect fix.

Fixes: 93efb0c6 ("octeontx2-pf: Fix out-of-bounds read in otx2_get_fecparam()")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/marvell/octeontx2/nic/otx2_ethtool.c

@@ -968,7 +968,7 @@ static int otx2_get_fecparam(struct net_device *netdev,
 		if (!rsp->fwdata.supported_fec)
 			fecparam->fec = ETHTOOL_FEC_NONE;
 		else
-			fecparam->fec = fec[rsp->fwdata.supported_fec - 1];
+			fecparam->fec = fec[rsp->fwdata.supported_fec];
 	}
 	return 0;
 }