[kws] update cross_entropy loss (#62)

* [kws] update cross_entropy loss

replace nn.CrossEntropyLoss() with F.cross_entropy()

* format

kws/model/loss.py

@@ -13,7 +13,7 @@
 # limitations under the License.
 
 import torch
-import torch.nn as nn
+import torch.nn.functional as F
 
 from kws.utils.mask import padding_mask
 
@@ -105,8 +105,7 @@ def cross_entropy(logits: torch.Tensor, target: torch.Tensor):
         (float): loss of current batch
         (float): accuracy of current batch
     """
-    cross_entropy = nn.CrossEntropyLoss()
-    loss = cross_entropy(logits, target)
+    loss = F.cross_entropy(logits, target)
     acc = acc_frame(logits, target)
     return loss, acc