xgene: Don't fail probe, if there is no clk resource for SGMII interfaces

This change fixes following problem

[    1.827940] xgene-enet: probe of 1f210030.ethernet failed with error -2

which leads to a missing ethernet interface (reproducable at least on
Gigabyte MP30-AR0 and APM Mustang systems).

The check for a valid clk resource fails, because DT doesn't provide a
clock for sgenet1. But the driver doesn't use this clk, if the ethernet
port is connected via SGMII. Therefore this patch avoids probing for clk
on SGMII interfaces.

Fixes: 9aea7779 ("drivers: net: xgene: Fix crash on DT systems")
Signed-off-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/apm/xgene/xgene_enet_main.c

@@ -1785,17 +1785,19 @@ static int xgene_enet_get_resources(struct xgene_enet_pdata *pdata)
 
 	xgene_enet_gpiod_get(pdata);
 
+	if (pdata->phy_mode != PHY_INTERFACE_MODE_SGMII) {
 		pdata->clk = devm_clk_get(&pdev->dev, NULL);
 		if (IS_ERR(pdata->clk)) {
-		/* Abort if the clock is defined but couldn't be retrived.
-		 * Always abort if the clock is missing on DT system as
-		 * the driver can't cope with this case.
+			/* Abort if the clock is defined but couldn't be
+			 * retrived. Always abort if the clock is missing on
+			 * DT system as the driver can't cope with this case.
 			 */
 			if (PTR_ERR(pdata->clk) != -ENOENT || dev->of_node)
 				return PTR_ERR(pdata->clk);
 			/* Firmware may have set up the clock already. */
 			dev_info(dev, "clocks have been setup already\n");
 		}
+	}
 
 	if (pdata->phy_mode != PHY_INTERFACE_MODE_XGMII)
 		base_addr = pdata->base_addr - (pdata->port_id * MAC_OFFSET);