[Bugfix] Fix Var Length Batched Padding in Granite Speech (#31906)

Signed-off-by: Alex-Brooks <Alex.Brooks@ibm.com>

vllm/model_executor/models/granite_speech.py

@@ -672,7 +672,13 @@ class GraniteSpeechForConditionalGeneration(
 
         else:
             # Otherwise we have a list of tensors, which are almost certainly
-            # differing in their respective numbers of audio features;
+            # differing in their respective numbers of audio features; when
+            # passed as a batch, we expect a list of 2D var len input features
+            # so unsqueeze them.
+            input_features = [
+                feat.unsqueeze(dim=0) for feat in input_features if feat.ndim == 2
+            ]
+
             # stack them into a 3D tensor of size [bsz, most_num_features, 160].
             input_features = self._pad_and_stack_input_features(
                 input_features,
@@ -724,13 +730,12 @@ class GraniteSpeechForConditionalGeneration(
 
         Args:
             input_features: list[torch.Tensor]
-                Input features to be coerced into a tensor.
+                3D Input features to be coerced into a tensor.
         Returns:
             torch.Tensor: Tensor of shape [bsz, num_features, 160], where
             num_features is the max number of features of any entry in the
             batch.
         """
-        # Input features are of shape [bsz, num_features, 160]
         feat_lens = [feats.shape[1] for feats in input_features]
         padding = [max(feat_lens) - length for length in feat_lens]
         # TODO (Alex) - Validate that it's okay to zero pad like this;