cpu: Assert asidx_from_attrs return value in range

Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NRichard Henderson <richard.henderson@linaro.org>

include/qom/cpu.h

@@ -620,11 +620,13 @@ static inline hwaddr cpu_get_phys_page_debug(CPUState *cpu, vaddr addr)
 static inline int cpu_asidx_from_attrs(CPUState *cpu, MemTxAttrs attrs)
 {
     CPUClass *cc = CPU_GET_CLASS(cpu);
+    int ret = 0;
 
     if (cc->asidx_from_attrs) {
-        return cc->asidx_from_attrs(cpu, attrs);
+        ret = cc->asidx_from_attrs(cpu, attrs);
+        assert(ret < cpu->num_ases && ret >= 0);
     }
-    return 0;
+    return ret;
 }
 #endif