target-microblaze: mmu: Make TLBSX write-only

Make TLBSX write-only and guest-error log reads from it.
Reviewed-by: NAlistair Francis <alistair.francis@wdc.com>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Signed-off-by: NEdgar E. Iglesias <edgar.iglesias@xilinx.com>

target/microblaze/mmu.c

@@ -182,7 +182,7 @@ done:
 uint32_t mmu_read(CPUMBState *env, uint32_t rn)
 {
     unsigned int i;
-    uint32_t r;
+    uint32_t r = 0;
 
     if (env->mmu.c_mmu < 2 || !env->mmu.c_mmu_tlb_access) {
         qemu_log_mask(LOG_GUEST_ERROR, "MMU access on MMU-less system\n");
@@ -211,6 +211,9 @@ uint32_t mmu_read(CPUMBState *env, uint32_t rn)
             }
             r = env->mmu.regs[rn];
             break;
+        case MMU_R_TLBSX:
+            qemu_log_mask(LOG_GUEST_ERROR, "TLBSX is write-only.\n");
+            break;
         default:
             r = env->mmu.regs[rn];
             break;