fio2gnuplot: Adding filename as title for 2D graphs

While plotting 2D graphs, it's pretty handy to keep the filename as
title for the plotting trace. This way, the png file still keep the
original filename used for plotting.
diff --git a/tools/plot/fio2gnuplot.py b/tools/plot/fio2gnuplot.py
index b5f70a0..800c334 100755
--- a/tools/plot/fio2gnuplot.py
+++ b/tools/plot/fio2gnuplot.py
@@ -98,7 +98,7 @@
                 smooth_filename = "%s-2Dsmooth" % (png_file)
                 trend_filename = "%s-2Dtrend" % (png_file)
                 avg  = average(disk_perf[pos])
-                f.write("call \'%s/graph2D.gpm\' \'%s' \'%s\' \'\' \'%s\' \'%s\' \'%s\' \'%s\' \'%f\'\n" % (gpm_dir,title,tmp_filename,raw_filename,mode,smooth_filename,trend_filename,avg))
+                f.write("call \'%s/graph2D.gpm\' \'%s' \'%s\' \'%s\' \'%s\' \'%s\' \'%s\' \'%s\' \'%f\'\n" % (gpm_dir,title,tmp_filename,fio_data_file[pos],raw_filename,mode,smooth_filename,trend_filename,avg))
                 pos = pos +1
 
 	# Plotting comparing graphs doesn't have a meaning unless if there is at least 2 traces