normalize label indent

1 space is most common in the source; this fixes some mixed cases within
lossless files, likely from clang-format

Change-Id: I504206d5bf418781d4131ee73570ecee4e0a69a1

src/enc/backward_references_cost_enc.c

@@ -675,7 +675,7 @@ static int BackwardReferencesHashChainDistanceOnly(
   }
 
   ok = !refs->error_;
-Error:
+ Error:
   if (cc_init) VP8LColorCacheClear(&hashers);
   CostManagerClear(cost_manager);
   WebPSafeFree(cost_model);