Handle absent weights_compression_ration when printing

Change-Id: Iafb31af73d80adcc901b241c34dda78be360bc14
Signed-off-by: Henrik G Olsson <henrik.olsson@arm.com>
diff --git a/ethosu/vela/stats_writer.py b/ethosu/vela/stats_writer.py
index 3d92d2c..9ccee72 100644
--- a/ethosu/vela/stats_writer.py
+++ b/ethosu/vela/stats_writer.py
@@ -327,7 +327,7 @@
         )
         print(file=f)
 
-    if weights_compression_ratio != 0:
+    if weights_compression_ratio:
         print(
             f"Weights Compression Ratio                {weights_compression_ratio:12.2f}", file=f,
         )