fix: wrong module name

[dixilo]

Description

This is a bug fix in plugin.py

Motivation and Context

plugin.py has wrong path to the PCR500MA module, preventing docker container boot up correctly.

How Has This Been Tested?

Confirmed that ocs-agent-cli --instance-id stimulator-pcr500ma works correctly.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.