docs: Fix uniunstall to uninstall typo in AJA README

[nakanoh]

docs: Fix typo in AJA plugin README

Change "uniunstall" to "uninstall" in the Linux kernel module uninstallation instructions

Description

This PR fixes a typographical error in the AJA plugin README. The word "uniunstall" is corrected to "uninstall" in the instructions for removing the Linux kernel module.

No other content was changed.

Motivation and Context

This change improves the clarity and professionalism of the documentation by correcting a simple spelling error. It helps users follow the correct instructions without confusion.

How Has This Been Tested?

• Verified the change in the documentation file (plugins/aja/README.md)
• Confirmed that the instructions are now correct and clear
• No code or functional changes, so no additional testing required

Types of changes

• [x] Documentation (a change to documentation pages)