mctp: Fix incorrect tx flow invalidation condition in mctp-i2c

Previously, the condition for invalidating the tx flow in
mctp_i2c_invalidate_tx_flow() checked if `rc` was nonzero.
However, this could incorrectly trigger the invalidation
even when `rc > 0` was returned as a success status.

This patch updates the condition to explicitly check for `rc < 0`,
ensuring that only error cases trigger the invalidation.

Signed-off-by: Daniel Hsu <Daniel-Hsu@quantatw.com>
Reviewed-by: Jeremy Kerr <jk@codeconstruct.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/mctp/mctp-i2c.c

@@ -537,7 +537,7 @@ static void mctp_i2c_xmit(struct mctp_i2c_dev *midev, struct sk_buff *skb)
 		rc = __i2c_transfer(midev->adapter, &msg, 1);
 
 		/* on tx errors, the flow can no longer be considered valid */
-		if (rc)
+		if (rc < 0)
 			mctp_i2c_invalidate_tx_flow(midev, skb);
 
 		break;