s390/test_unwind: require that unwinding ended successfully

Currently unwinder test passes if unwinding results contain unwindme_func2
and unwindme_func1 functions.
Now that unwinder reports success upon reaching task pt_regs, check
that unwinding ended successfully in every test.

Acked-by: Heiko Carstens <[e-mail]>
Signed-off-by: Vasily Gorbik <[e-mail]>

arch/s390/lib/test_unwind.c

···
 	}
 
 	/* Check the results. */
+	if (unwind_error(&state)) {
+		pr_err("unwind error\n");
+		ret = -EINVAL;
+	}
 	if (!seen_func2_func1) {
 		pr_err("unwindme_func2 and unwindme_func1 not found\n");
 		ret = -EINVAL;