CLPF unit test: Only test damping values that are actually used

Change-Id: I1320b9e2f57363686340f066e5366be385daa493

test/clpf_test.cc

@@ -115,7 +115,7 @@ void test_clpf(int w, int h, int depth, int iterations,
   for (count = 0; count < iterations; count++) {
     for (level = 0; level < (1 << depth) && !error; level++) {
       for (bits = 1; bits <= depth && !error; bits++) {
-        for (damp = 4; damp <= depth && !error; damp++) {
+        for (damp = 4; damp < depth - 1 && !error; damp++) {
           for (int i = 0; i < size * size; i++)
             s[i] = clamp((rnd.Rand16() & ((1 << bits) - 1)) + level, 0,
                          (1 << depth) - 1);