target/loongarch: Fix raise_mmu_exception() set wrong exception_index

When the address is invalid address, We should set exception_index
according to MMUAccessType, and EXCCODE_ADEF need't update badinstr.
Otherwise, The system enters an infinite loop. e.g:
run test.c on system mode
test.c:
    #include<stdio.h>

    void (*func)(int *);

    int main()
    {
        int i = 8;
        void *ptr = (void *)0x4000000000000000;
        func = ptr;
        func(&i);
        return 0;
    }

Signed-off-by: Song Gao <gaosong@loongson.cn>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20221101073210.3934280-2-gaosong@loongson.cn>

target/loongarch/cpu.c

@@ -177,6 +177,7 @@ static void loongarch_cpu_do_interrupt(CPUState *cs)
         }
         QEMU_FALLTHROUGH;
     case EXCCODE_PIF:
+    case EXCCODE_ADEF:
         cause = cs->exception_index;
         update_badinstr = 0;
         break;

target/loongarch/tlb_helper.c

@@ -229,7 +229,8 @@ static void raise_mmu_exception(CPULoongArchState *env, target_ulong address,
     switch (tlb_error) {
     default:
     case TLBRET_BADADDR:
-        cs->exception_index = EXCCODE_ADEM;
+        cs->exception_index = access_type == MMU_INST_FETCH
+                              ? EXCCODE_ADEF : EXCCODE_ADEM;
         break;
     case TLBRET_NOMATCH:
         /* No TLB match for a mapped address */
@@ -643,7 +644,7 @@ bool loongarch_cpu_tlb_fill(CPUState *cs, vaddr address, int size,
     CPULoongArchState *env = &cpu->env;
     hwaddr physical;
     int prot;
-    int ret = TLBRET_BADADDR;
+    int ret;
 
     /* Data access */
     ret = get_physical_address(env, &physical, &prot, address,