s390/unwind: report an error if pt_regs are not on stack

If unwinder is looking at pt_regs which is not on stack then something
went wrong and an error has to be reported rather than successful
unwinding termination.

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/kernel/unwind_bc.c

@@ -76,7 +76,7 @@ bool unwind_next_frame(struct unwind_state *state)
 			/* No back-chain, look for a pt_regs structure */
 			sp = state->sp + STACK_FRAME_OVERHEAD;
 			if (!on_stack(info, sp, sizeof(struct pt_regs)))
-				goto out_stop;
+				goto out_err;
 			regs = (struct pt_regs *) sp;
 			if (READ_ONCE_NOCHECK(regs->psw.mask) & PSW_MASK_PSTATE)
 				goto out_stop;