fix: unexpected keyword argument reorder

[superpung]

In the definition of the VerilogGraphGenerator class, one of the arguments of its generate method is do_reorder:

Pyverilog/pyverilog/dataflow/graphgen.py

Line 57 in 81838bc

def generate(self, signalname, identical=False, walk=True, step=1, do_reorder=False, delay=False):

However, in the example_graphgen.py file, this argument is mistakenly referred to as reorder.

Pyverilog/examples/example_graphgen.py

Lines 100 to 101 in 81838bc

	graphgen.generate(target, walk=options.walk, identical=options.identical,
	step=options.step, reorder=options.reorder, delay=options.delay)

So when running python3 pyverilog/examples/example_graphgen.py -t top -s top.led test.v, I encountered error messages that are as follows:

Generating LALR tables
WARNING: 183 shift/reduce conflicts
Traceback (most recent call last):
  File "/path/to/pyverilog-demo/pyverilog/examples/example_graphgen.py", line 107, in <module>
    main()
  File "/path/to/pyverilog-demo/pyverilog/examples/example_graphgen.py", line 100, in main
    graphgen.generate(target, walk=options.walk, identical=options.identical,
TypeError: VerilogGraphGenerator.generate() got an unexpected keyword argument 'reorder'