Update dmx_perplexity.py

making sure seq_len is a multiple of stride

dmx_perplexity.py

@@ -102,6 +102,7 @@ class DmxPerplexity(evaluate.Metric):
 
         stride = max_seq_len
         seq_len = encodings.input_ids.size(1)
+        seq_len = (seq_len // stride) * stride
 
         nlls = []
         prev_end_loc = 0