fix(accel_brake_map_calibrator): fix view_statistics script

[tkimura4]

Description

I fixed view_statistics.py script in the accel_brake_map_calibrator package.

After:

Tests performed

Before:
The script causes the following error.

After:
The script can output matplot image

Effects on system behavior

It does not affect autonomous driving behavior.

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[shmpwk]

LGTM

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (010523f) 15.10% compared to head (07c4814) 15.10%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3793   +/-   ##
=======================================
  Coverage   15.10%   15.10%           
=======================================
  Files        1332     1332           
  Lines       94823    94823           
  Branches    27009    27009           
=======================================
  Hits        14321    14321           
  Misses      64813    64813           
  Partials    15689    15689           

Flag	Coverage Δ		*Carryforward flag
differential	0.00% <ø> (?)
total	15.10% <ø> (ø)		Carriedforward from 010523f

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[1222-takeshi]

LGTM