nfp: use the correct index for link speed table

sts variable is holding link speed as well as state.  We should
be using ls to index into ls_to_ethtool.

Fixes: 265aeb5 ("nfp: add support for .get_link_ksettings()")
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: Jakub Kicinski

drivers/net/ethernet/netronome/nfp/nfp_net_ethtool.c

@@ -333,7 +333,7 @@ nfp_net_get_link_ksettings(struct net_device *netdev,
 	    ls >= ARRAY_SIZE(ls_to_ethtool))
 		return 0;
 
-	cmd->base.speed = ls_to_ethtool[sts];
+	cmd->base.speed = ls_to_ethtool[ls];
 	cmd->base.duplex = DUPLEX_FULL;
 
 	return 0;