[FP8] unsqueeze scale to make it compatible with torch.compile (#6040)

colossalai/quantization/fp8.py

@@ -56,7 +56,7 @@ def cast_to_fp8(inp: torch.Tensor, fp8_format="e4m3", per_channel_scale=False) -
             scale_inv = 1.0 / scale
 
     ret = (scale * inp.float()).to(fp8_type)
-    return ret, scale_inv
+    return ret, torch.unsqueeze(scale_inv, dim=0)
 
 
 def cast_from_fp8(