gpt2 multi-gpu fix (#23149)

Co-authored-by: Prof. Peter Schneider-Kamp <jps@ordbogen.com>

src/transformers/models/gpt2/modeling_gpt2.py

@@ -1670,9 +1670,9 @@ class GPT2ForQuestionAnswering(GPT2PreTrainedModel):
         if start_positions is not None and end_positions is not None:
             # If we are on multi-GPU, split add a dimension
             if len(start_positions.size()) > 1:
-                start_positions = start_positions.squeeze(-1)
+                start_positions = start_positions.squeeze(-1).to(start_logits.device)
             if len(end_positions.size()) > 1:
-                end_positions = end_positions.squeeze(-1)
+                end_positions = end_positions.squeeze(-1).to(end_logits.device)
             # sometimes the start/end positions are outside our model inputs, we ignore these terms
             ignored_index = start_logits.size(1)
             start_positions = start_positions.clamp(0, ignored_index)