apply flake8 linting #19

# to view logs

Job	Run time
Get testbenches	2s
testbench (umi/testbench/test_fifo.py)	1m 1s
testbench (umi/testbench/test_mem_agent.py)	1m 11s
testbench (umi/testbench/test_crossbar.py)	2m 2s
testbench (umi/testbench/test_fifo_flex.py)	56s
testbench (umi/testbench/test_regif.py)	1m 17s
testbench (lumi/testbench/test_lumi.py)	2m 9s
testbench (lumi/testbench/test_lumi_rnd.py)	2m 23s
testbench (utils/testbench/test_umi_address_remap.py)	1m 7s
testbench (utils/testbench/test_umi_packet_merge_greedy.py)	1m 19s
testbench (utils/testbench/test_umi2tl_np.py)	1m 22s
	14m 49s

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