Fix bug storing encoded NPU weight UUIDs

Fix bug when storing the encoded NPU weight UUID in the
NPU performance estimation.

Signed-off-by: Jonas Ohlsson <jonas.ohlsson@arm.com>
Change-Id: I92127b0020f12352d923c0c9aa2b6f47e6110764
diff --git a/ethosu/vela/npu_performance.py b/ethosu/vela/npu_performance.py
index 450fa7b..34530ae 100644
--- a/ethosu/vela/npu_performance.py
+++ b/ethosu/vela/npu_performance.py
@@ -753,7 +753,7 @@
             # Save UUIDs of encoded_npu_weight so only unique instances of tensors are used to calculate weights
             if encoded_npu_weight and (encoded_npu_weight.equivalence_id not in encoded_npu_weight_uuids):
 
-                encoded_npu_weight_uuids.add(encoded_npu_weight)
+                encoded_npu_weight_uuids.add(encoded_npu_weight.equivalence_id)
                 total_encoded_weight_size += len(encoded_npu_weight.buffer)
 
             total_bws += bws