net: ti: icssg-prueth: Fix signedness bug in prueth_init_tx_chns()

The "tx_chn->irq" variable is unsigned so the error checking does not
work correctly.

Fixes: 128d5874 ("net: ti: icssg-prueth: Add ICSSG ethernet driver")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Roger Quadros <rogerq@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/ti/icssg/icssg_prueth.c

@@ -316,12 +316,14 @@ static int prueth_init_tx_chns(struct prueth_emac *emac)
 			goto fail;
 		}
 
-		tx_chn->irq = k3_udma_glue_tx_get_irq(tx_chn->tx_chn);
-		if (tx_chn->irq <= 0) {
+		ret = k3_udma_glue_tx_get_irq(tx_chn->tx_chn);
+		if (ret <= 0) {
+			if (!ret)
 				ret = -EINVAL;
 			netdev_err(ndev, "failed to get tx irq\n");
 			goto fail;
 		}
+		tx_chn->irq = ret;
 
 		snprintf(tx_chn->name, sizeof(tx_chn->name), "%s-tx%d",
 			 dev_name(dev), tx_chn->id);