use softmax_last_dim (metal and cuda kernel) in llama attention layer (#2572)

candle-transformers/src/models/llama.rs

@@ -341,7 +341,8 @@ impl CausalSelfAttention {
                 let mask = cache.mask(seq_len)?.broadcast_as(att.shape())?;
                 masked_fill(&att, &mask, f32::NEG_INFINITY)?
             };
-            let att = candle_nn::ops::softmax(&att, D::Minus1)?;
+
+            let att = candle_nn::ops::softmax_last_dim(&att)?;
             // Convert to contiguous as matmul doesn't support strided vs for now.
             att.matmul(&v.contiguous()?)?.to_dtype(in_dtype)?
         };