net: thunderx: avoid dereferencing xcv when NULL

This fixes the following smatch and coccinelle warnings:

  drivers/net/ethernet/cavium/thunder/thunder_xcv.c:119 xcv_setup_link() error: we previously assumed 'xcv' could be null (see line 118) [smatch]
  drivers/net/ethernet/cavium/thunder/thunder_xcv.c:119:16-20: ERROR: xcv is NULL but dereferenced. [coccinelle]

Fixes: 6465859 ("net: thunderx: Add RGMII interface type support")
Signed-off-by: Vincent Stehlé <vincent.stehle@laposte.net>
Cc: Sunil Goutham <sgoutham@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/cavium/thunder/thunder_xcv.c

@@ -116,8 +116,7 @@ void xcv_setup_link(bool link_up, int link_speed)
 	int speed = 2;
 
 	if (!xcv) {
-		dev_err(&xcv->pdev->dev,
-			"XCV init not done, probe may have failed\n");
+		pr_err("XCV init not done, probe may have failed\n");
 		return;
 	}