Fix the powerflex driver deployment issue

[ashleyvjoy]

Description

There was a regression caused in powerflex driver deployment using minimal CR due to the changes that went in powerflex.go as part of this PR: #703. As a result the node pods were not coming up due to Error: couldn't find key MDM in Secret vxflexos/vxflexos-config

This PR is to address and fix the driver deployment issue with minimal CR

GitHub Issues

List the GitHub issues impacted by this PR:

| GitHub Issue # |
| dell/csm#1449 |

Checklist:

• I have performed a self-review of my own code to ensure there are no formatting, vetting, linting, or security issues
• I have verified that new and existing unit tests pass locally with my changes
• I have not allowed coverage numbers to degenerate
• I have maintained at least 90% code coverage
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have maintained backward compatibility

How Has This Been Tested?

• Deployed the powerflex driver using both minimal CR and existing CR and verified that pods are up and running