[Docs][querydb] Fix comment in UseAfterFree query

[HamzaMouhcine]

In the file querydb/src/main/scala/io/joern/scanners/c/UseAfterFree.scala, the free-follows-value-reuse query has a comment in the "the query does not match" examples. The comment states that the return x is not post-dominated by the free call, I believe this is not what the author meant as this statement is not relevant to what the query is doing. This could confuse users. I believe the author wanted to write the following comment instead return x doesn't post-dominate the free call.

I opened a pr with a fix here.