Clean up a comment.

SetProcessDEPPolicy() is the API; PSetProcessDEPPolicy is just a local
pointer variable that either points to that API's implementation (if
it's available) or is null (if it isn't).

Change-Id: I676fbb75019e32af511cefa6f1c7b7124ac9d8e8
Reviewed-on: https://code.wireshark.org/review/2735
Reviewed-by: Guy Harris <guy@alum.mit.edu>