[MLBEDSW-4414] Fix verbose-operators for multiple custom ops

Fixed exception for --verbose-operators option when there are
multiple custom operators in the network.

Signed-off-by: Fredrik Svedberg <fredrik.svedberg@arm.com>
Change-Id: I5ab743d96a4e0367818fbe46cc47896c691d888c
diff --git a/ethosu/vela/nn_graph.py b/ethosu/vela/nn_graph.py
index 1973487..2d4b0c8 100644
--- a/ethosu/vela/nn_graph.py
+++ b/ethosu/vela/nn_graph.py
@@ -337,10 +337,13 @@
                 attrs["kshape"] = [kshape[0], kshape[1]]
             attrs["type"] = op.type.name
             attrs.pop("use_cudnn_on_gpu", None)
+            custom_options = attrs.pop("custom_options", None)
             if attrs not in unique_ops:
                 unique_ops.append(attrs)
                 # print attributes in human readable format
                 a = attrs.copy()
+                if custom_options is not None:
+                    a["custom_options"] = custom_options
                 s = a.pop("type")
                 data_format = a.pop("data_format", None)
                 if data_format and data_format != b"NHWC":