Fix the inplace sign operation

Author: yongchanghao

lion/lion_pytorch.py

@@ -78,10 +78,7 @@ def step(self, closure=None):
         # Weight update
         update = exp_avg * beta1 + grad * (1 - beta1)
 
-        p.add_(torch.sign(update), alpha=-group['lr'], inplace=True)
-        #This has been made more efficient by using the torch.sign function's inplace mode. 
-        #This will prevent the need to create a new tensor for the updated parameter, 
-        #which can save a significant amount of time for large models. 
+        p.add_(update.sign_(), alpha=-group['lr'])
 
         # Decay the momentum running average coefficient
         exp_avg.mul_(beta2).add_(grad, alpha=1 - beta2)