package.xml: Fix typo in comments

The sorting priority is from highest to lowes, so fixing the comment on
various package.xml files.

Change-Id: I76330ec0e7b2f4555951beb21820e3fcb3146cd4
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>