[MLBEDSW-3813] Fix LSTM operator pass through

Fixed pass through of LSTM operator.

Change-Id: I23140c69ab6cdc83f6bb8129256b4cc6a7c5ffac
Signed-off-by: Fredrik Svedberg <fredrik.svedberg@arm.com>
diff --git a/ethosu/vela/tensor.py b/ethosu/vela/tensor.py
index b7d4307..97885d0 100644
--- a/ethosu/vela/tensor.py
+++ b/ethosu/vela/tensor.py
@@ -341,6 +341,7 @@
         "bandwidth_shape",
         "dtype",
         "name",
+        "is_variable",
         "ops",
         "consumer_list",
         "values",
@@ -378,6 +379,7 @@
         self.bandwidth_shape = shape
         self.dtype = dtype
         self.name = name
+        self.is_variable = False
         self.equivalence_id: UUID = uuid.uuid4()
 
         self.ops: List[Operation] = []