HID: fix reversed logic in disconnect testing of hiddev

The logic for testing for disconnection is reversed in an ioctl leading
to false reports of disconnection.
Signed-off-by: NOliver Neukum <oneukum@suse.de>
Tested-by: NFolkert van Heusden <folkert@vanheusden.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

drivers/hid/usbhid/hiddev.c

@@ -656,7 +656,7 @@ static long hiddev_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 
 	case HIDIOCGSTRING:
 		mutex_lock(&hiddev->existancelock);
-		if (!hiddev->exist)
+		if (hiddev->exist)
 			r = hiddev_ioctl_string(hiddev, cmd, user_arg);
 		else
 			r = -ENODEV;