Bug fix when initialising PWM 2,3 or 4

git-svn-id: https://chibios.svn.sourceforge.net/svnroot/chibios/trunk@5354 35acf78f-673a-0410-8e92-d51de3d6d3f4
git-svn-id: https://chibios.svn.sourceforge.net/svnroot/chibios/trunk@5355 35acf78f-673a-0410-8e92-d51de3d6d3f4