Fixed missing op import

model/sg2_model.py

@@ -8,6 +8,8 @@ from torch import nn
 from torch.nn import functional as F
 from torch.autograd import Function
 
+from op import conv2d_gradfix
+
 if torch.cuda.is_available():
     from op.fused_act import FusedLeakyReLU, fused_leaky_relu
     from op.upfirdn2d import upfirdn2d