PPC: booke206: Check for TLB overrun

Our internal helpers to fetch TLB entries were not able to tell us
that an entry doesn't even exist. Pass an error out if we hit such
a case to not accidently pass beyond the TLB array.

Signed-off-by: Alexander Graf <agraf@suse.de>

target-ppc/helper.c

@@ -1448,6 +1448,9 @@ static int mmubooke206_get_physical_address(CPUState *env, mmu_ctx_t *ctx,
 
         for (j = 0; j < ways; j++) {
             tlb = booke206_get_tlbm(env, i, address, j);
+            if (!tlb) {
+                continue;
+            }
             ret = mmubooke206_check_tlb(env, tlb, &raddr, &ctx->prot, address,
                                         rw, access_type);
             if (ret != -1) {