change elementwise perf baseline

Author: Natalia Gimelshein

python/test/regression/test_performance.py

@@ -128,7 +128,7 @@ def _add(x_ptr, y_ptr, output_ptr, n_elements,
         1024 * 16: 0.0219,
         1024 * 64: 0.0791,
         1024 * 256: 0.243,
-        1024 * 1024: 0.534,
+        1024 * 1024: 0.520,
         1024 * 4096: 0.796,
         1024 * 16384: 0.905,
         1024 * 65536: 0.939,