net: pcs: xpcs: Return EINVAL in the internal methods

In particular the xpcs_soft_reset() and xpcs_do_config() functions
currently return -1 if invalid auto-negotiation mode is specified. That
value might be then passed to the generic kernel subsystems which require
a standard kernel errno value. Even though the erroneous conditions are
very specific (memory corruption or buggy driver implementation) using a
hard-coded -1 literal doesn't seem correct anyway especially when it comes
to passing it higher to the network subsystem or printing to the system
log.  Convert the hard-coded error values to -EINVAL then.
Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Tested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/pcs/pcs-xpcs.c

@@ -292,7 +292,7 @@ static int xpcs_soft_reset(struct dw_xpcs *xpcs,
 		dev = MDIO_MMD_VEND2;
 		break;
 	default:
-		return -1;
+		return -EINVAL;
 	}
 
 	ret = xpcs_write(xpcs, dev, MDIO_CTRL1, MDIO_CTRL1_RESET);
@@ -889,7 +889,7 @@ int xpcs_do_config(struct dw_xpcs *xpcs, phy_interface_t interface,
 			return ret;
 		break;
 	default:
-		return -1;
+		return -EINVAL;
 	}
 
 	if (compat->pma_config) {