Fix himsBrailleDisplayDriver code error

[EdKweon]

Link to issue number:

Summary of the issue:

There is issue that undefined class member variable.

Description of user facing changes

User can use NVDA Hims Display driver normally. (HID, Bulk, and Serial)

Description of development approach

Nothing to approach. Just fix error that not defined class member variable.

Testing strategy:

lint, system, unit

Known issues with pull request:

#16279

Code Review Checklist:

• Documentation:
  • Change log entry
  • User Documentation
  • Developer / Technical Documentation
  • Context sensitive help for GUI changes
• Testing:
  • Unit tests
  • System (end to end) tests
  • Manual testing
• UX of all users considered:
  • Speech
  • Braille
  • Low Vision
  • Different web browsers
  • Localization in other languages / culture than English
• API is compatible with existing add-ons.
• Security precautions taken.