boost ring queue: use % to wrap the index

For power of 2, it is replaced with a single and instruction. If it potentially faster
than branch. But it worths a benchmark

plugins/GSdx/boost_spsc_queue.hpp

@@ -91,11 +91,12 @@ public:
     {
         size_t ret = arg + 1;
 #if 0
+        // Initial boost code
         while (unlikely(ret >= max_size))
-#else
-        while (ret >= max_size)
-#endif
             ret -= max_size;
+#else
+        ret %= max_size;
+#endif
         return ret;
     }