tools: Fix a syntax error in plot-timer-events

tools/plot-timer-events

Index: tools/plot-timer-events
diff --git a/tools/plot-timer-events b/tools/plot-timer-events
index 15f28ac22b5b849314ff745b305be51a75b9a194..da2e823c14df613f30034ca693ed82b2963268d0 100755
--- a/tools/plot-timer-events
+++ b/tools/plot-timer-events
@@ -70,10 +70,9 @@ if test "$contains" -eq 0; then
   rm $calibration_log
 
   # Overhead in picoseconds.
-  options=--distortion=
-  options+=`echo "1000*(($t_1_end - $t_1_start) - ($t_2_end - $t_2_start)) \
+  distortion=`echo "1000*(($t_1_end - $t_1_start) - ($t_2_end - $t_2_start)) \
               / ($n_1 - $n_2)" | bc`
-  echo $options
+  options="--distortion=$distortion"
 fi
 
 cat $log_file |