Add a ; to the newly defined KEY_SYMBOL struct

Description

SpamBinBuild.py cannot successfully build without this bugfix.

[ ] Impacts functionality?
- Functionality - Does the change ultimately impact how firmware functions?
- Examples: Add a new library, publish a new PPI, update an algorithm, ...
[ ] Impacts security?
- Security - Does the change have a direct security impact on an application, flow, or firmware?
- Examples: Crypto algorithm change, buffer overflow fix, parameter validation improvement, ...
[ ] Breaking change?
- Breaking change - Will anyone consuming this change experience a break in build or boot behavior?
- Examples: Add a new library class, move a module to a different repo, call a function in a new library class in a pre-existing module, ...
[ ] Includes tests?
- Tests - Does the change include any explicit test code?
- Examples: Unit tests, integration tests, robot tests, ...
[ ] Includes documentation?
- Documentation - Does the change contain explicit documentation additions outside direct code modifications (and comments)?
- Examples: Update readme file, add feature readme file, link to documentation on an a separate Web page, ...