MLBEDSW-2637 Utilise new tensor and operator funcs

add_input_tensor, set_output_tensor, create_const_tensor and
create_reshape_tensor have recently been added.
This replaces all found existing instances with these new helper
functions

Signed-off-by: Michael McGeagh <michael.mcgeagh@arm.com>
Change-Id: If33be8dbf237b2087b562b03cdeb51da1f99a786
diff --git a/ethosu/vela/npu_serialisation.py b/ethosu/vela/npu_serialisation.py
index 030503d..c6b0d87 100644
--- a/ethosu/vela/npu_serialisation.py
+++ b/ethosu/vela/npu_serialisation.py
@@ -149,8 +149,7 @@
 
 def add_const_tens_to_startup_cascaded_pass(startup_cps, tens):
     op = Operation("Const", tens.name + "_const")
-    op.outputs = [tens]
-    tens.ops = [op]
+    op.set_output_tensor(tens)
     startup_cps.passes[0].ops.insert(0, op)
     startup_cps.passes[0].outputs.insert(0, tens)
     startup_cps.outputs.insert(0, tens)