opal: fix debug message on failed sed-opal ioctl.

ioctl syscall always returns -1 on error (see ioctl(2)).
On error the actual reason is reported via errno varible.
Let's store the original errno code in the variable
so that it can be printed out in debug mode.

Before this fix the debug message always reported "Operation not
permited" (the translation of errno EPERM (1)).

lib/luks2/hw_opal/hw_opal.c

@@ -242,6 +242,8 @@ static int opal_ioctl(struct crypt_device *cd, int fd, unsigned long rq, void *a
 
 	opal_ioctl_debug(cd, rq, args, false, 0);
 	r = ioctl(fd, rq, args);
+	if (r < 0)
+		r = -errno;
 	opal_ioctl_debug(cd, rq, args, true, r);
 
 	return r;