s390x: s390_cpu_get_phys_page_debug has to return -1

If translation fails, we have to return -1. For now, we
would simply return the value last stored to raddr (if any).

This way, reading invalid memory via gdb will return values, although it
shouldn't.
Reviewed-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: NDavid Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>

target-s390x/helper.c

@@ -162,8 +162,9 @@ hwaddr s390_cpu_get_phys_page_debug(CPUState *cs, vaddr vaddr)
         vaddr &= 0x7fffffff;
     }
 
-    mmu_translate(env, vaddr, MMU_INST_FETCH, asc, &raddr, &prot, false);
-
+    if (mmu_translate(env, vaddr, MMU_INST_FETCH, asc, &raddr, &prot, false)) {
+        return -1;
+    }
     return raddr;
 }