refactor rotary embeddings

Author: DavidLandup0

keras_hub/src/models/smollm3/smollm3_layers.py

@@ -600,7 +600,7 @@ def call(
         batch_size = ops.shape(x)[0]
         seq_len = ops.shape(x)[1]
         positions = ops.arange(seq_len, dtype="float32")
-        positions + ops.cast(start_index, dtype="float32")
+        positions = positions + ops.cast(start_index, dtype="float32")
 
         inv_freq_expanded = ops.broadcast_to(
             inv_freq_expanded, (batch_size, ops.shape(self.inv_freq)[0], 1)