net: dsa: sja1105: Don't return a negative in u8 sja1105_stp_state_get

Dan Carpenter says:

The patch 640f763f: "net: dsa: sja1105: Add support for Spanning
Tree Protocol" from May 5, 2019, leads to the following static
checker warning:

        drivers/net/dsa/sja1105/sja1105_main.c:1073 sja1105_stp_state_get()
        warn: signedness bug returning '(-22)'

The caller doesn't check for negative errors anyway.

Fixes: 640f763f: ("net: dsa: sja1105: Add support for Spanning Tree Protocol")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/sja1105/sja1105_main.c

@@ -1070,7 +1070,11 @@ static u8 sja1105_stp_state_get(struct sja1105_private *priv, int port)
 		return BR_STATE_LEARNING;
 	if (mac[port].ingress && mac[port].egress && mac[port].dyn_learn)
 		return BR_STATE_FORWARDING;
-	return -EINVAL;
+	/* This is really an error condition if the MAC was in none of the STP
+	 * states above. But treating the port as disabled does nothing, which
+	 * is adequate, and it also resets the MAC to a known state later on.
+	 */
+	return BR_STATE_DISABLED;
 }
 
 /* For situations where we need to change a setting at runtime that is only