Update fenwick_tree_2d.cpp

Data Structures/fenwick_tree_2d.cpp

@@ -16,6 +16,6 @@ public:
 		for (int i = x; i > 0; i -= i & -i) {
 			for (int j = y; j > 0; j -= j & -j) ret += FT[i][j];
 		}
-	    return ans;
+		return ret;
 	}
 }