plot_utils: make pylint happier
plot_utils: make pylint happier

Cosmetic fixes to please pylint

Change-Id: I345e2f9e428dc890f67496171a2a28637eb94e46

sinkap/trappy,joelagnel/trappy,bjackman/trappy,ARM-software/trappy,ARM-software/trappy,joelagnel/trappy,bjackman/trappy,JaviMerino/trappy,derkling/trappy,JaviMerino/trappy,ARM-software/trappy,joelagnel/trappy,JaviMerino/trappy,ARM-software/trappy,derkling/trappy,derkling/trappy,sinkap/trappy,sinkap/trappy,joelagnel/trappy,bjackman/trappy,sinkap/trappy,bjackman/trappy