Fix compiler warnings: uninitialized variables.

- mpc601_block_address_translation will now return 0 for prot and pa when bat_hit is false (when the if statement is not positive during the for loop). The calling function doesn't care what prot and pa are when bat_hit is false, but we do this to remove the compiler warining.
- For tlb_flush_entry, the compiler thinks m might not always be in the range 0 to 5 so tlb1 and tlb2 might not get initialized by the switch statement. Add default to get around this warning.

cpu/ppc/ppcmmu.cpp

@@ -125,11 +125,11 @@ static BATResult mpc601_block_address_translation(uint32_t la)
 
             // logical to physical translation
             pa = bat_entry->phys_hi | (la & ~bat_entry->hi_mask);
-            break;
+            return BATResult{bat_hit, prot, pa};
         }
     }
 
-    return BATResult{bat_hit, prot, pa};
+    return BATResult{bat_hit, 0, 0};
 }
 
 /** PowerPC-style block address translation. */
@@ -742,6 +742,7 @@ void tlb_flush_entry(uint32_t ea)
             tlb1 = &dtlb1_mode2[0];
             tlb2 = &dtlb2_mode2[0];
             break;
+        default:
         case 5:
             tlb1 = &dtlb1_mode3[0];
             tlb2 = &dtlb2_mode3[0];