fix fullbench's LZ4_free()

tests/fullbench.c

@@ -160,7 +160,7 @@ static size_t BMK_findMaxMem(U64 requiredMem)
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 void* LZ4_malloc(size_t s) { return malloc(s); }
 void* LZ4_calloc(size_t s) { return calloc(1,s); }
-void  LZ4_free(void* p) { return free(p); }
+void  LZ4_free(void* p) { free(p); }
 
 
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