Fixed bug #551.

git-svn-id: svn://svn.code.sf.net/p/chibios/svn/branches/stable_2.6.x@7594 35acf78f-673a-0410-8e92-d51de3d6d3f4
Merge branch 'stable_2.6.x' into stable_2.6.x_with_Olimex_H405