Fixed bug in simulated PLL

See http://forums.parallax.com/showthread.php/157387
Fixed bug in simulated PLL (Nexys variant)

Adding the bugfix to the Nexys subdir as well.
Merge pull request #5 from andrewsil1/master

Add PLL bugfix to the Nexys4 variant as well.
(Sorry I forgot that directory in the previous commit -- JG)