Data Controls: Docs: Fix syntax errors and inaccurate usage example for dispatch data control

[aduth]

This pull request seeks to improve the documentation for the @wordpress/data-controls package in two ways:

• Fix an inaccuracy with the usage of dispatch as receiving multiple arguments (vs. the store key and returning an object of action dispatchers)
• Resolve syntax errors, notably with the generator function declaration

Testing Instructions:

As these changes purely impact documentation, there should be no runtime impact.

[nerrad]

Doh! Those were pretty bad errors, thanks for the fix!

[youknowriad]

So bad at being AFK :)