can: gs_usb: gs_make_candev(): clean up error handling

Introduce a label to free the allocated candev in case of an error and
make use of if. Fix a memory leak if the extended bit timing cannot be
read. Extend the error messages to print the number of the failing
channel and the symbolic error name.

Link: https://lore.kernel.org/all/20220921193902.575416-4-mkl@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/gs_usb.c

@@ -1100,8 +1100,8 @@ static struct gs_can *gs_make_candev(unsigned int channel,
 
 	if (rc) {
 		dev_err(&intf->dev,
-			"Couldn't get bit timing const for channel (err=%d)\n",
-			rc);
+			"Couldn't get bit timing const for channel %d (%pe)\n",
+			channel, ERR_PTR(rc));
 		return ERR_PTR(rc);
 	}
 
@@ -1215,9 +1215,9 @@ static struct gs_can *gs_make_candev(unsigned int channel,
 					  1000, GFP_KERNEL);
 		if (rc) {
 			dev_err(&intf->dev,
-				"Couldn't get extended bit timing const for channel (err=%d)\n",
-				rc);
-			return ERR_PTR(rc);
+				"Couldn't get extended bit timing const for channel %d (%pe)\n",
+				channel, ERR_PTR(rc));
+			goto out_free_candev;
 		}
 
 		strcpy(dev->data_bt_const.name, KBUILD_MODNAME);
@@ -1237,12 +1237,17 @@ static struct gs_can *gs_make_candev(unsigned int channel,
 
 	rc = register_candev(dev->netdev);
 	if (rc) {
-		free_candev(dev->netdev);
-		dev_err(&intf->dev, "Couldn't register candev (err=%d)\n", rc);
-		return ERR_PTR(rc);
+		dev_err(&intf->dev,
+			"Couldn't register candev for channel %d (%pe)\n",
+			channel, ERR_PTR(rc));
+		goto out_free_candev;
 	}
 
 	return dev;
+
+ out_free_candev:
+	free_candev(dev->netdev);
+	return ERR_PTR(rc);
 }
 
 static void gs_destroy_candev(struct gs_can *dev)