Undefined name: Typo in variable name sotrage_order --> storage_order (#3439)

Discovered via: __flake8 . --count --select=E9,F63,F72,F82 --show-source --statistics__

nnvm/python/nnvm/frontend/onnx.py

@@ -31,7 +31,7 @@ def onnx_storage_order2layout(storage_order):
     if storage_order not in (0, 1):
         raise tvm.error.OpAttributeInvalid('Mode of storage_order must be either 0 or 1')
 
-    return 'NCHW' if sotrage_order == 0 else 'NHWC'
+    return 'NCHW' if storage_order == 0 else 'NHWC'
 
 
 class OnnxOpConverter(object):