Staging: batman-adv: return -EFAULT on copy_to_user errors

copy_to_user() returns the number of bites remaining but we want to
return a negative error code here.
Signed-off-by: NDan Carpenter <error27@gmail.com>
Signed-off-by: NSven Eckelmann <sven.eckelmann@gmx.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/staging/batman-adv/device.c

@@ -196,7 +196,7 @@ ssize_t bat_device_read(struct file *file, char __user *buf, size_t count,
 	kfree(device_packet);
 
 	if (error)
-		return error;
+		return -EFAULT;
 
 	return sizeof(struct icmp_packet);
 }