xen/pvcalls-back: test for errors when calling backend_connect()

backend_connect() can fail, so switch the device to connected only if
no error occurred.

Fixes: 0a9c75c ("xen/pvcalls: xenbus state handling")
Cc: [email protected]
Signed-off-by: Juergen Gross <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Stefano Stabellini <[email protected]>
Signed-off-by: Boris Ostrovsky <[email protected]>

Author: jgross1

drivers/xen/pvcalls-back.c

@@ -1088,7 +1088,8 @@ static void set_backend_state(struct xenbus_device *dev,
 		case XenbusStateInitialised:
 			switch (state) {
 			case XenbusStateConnected:
-				backend_connect(dev);
+				if (backend_connect(dev))
+					return;
 				xenbus_switch_state(dev, XenbusStateConnected);
 				break;
 			case XenbusStateClosing: