Used toAsciiUpperCase() from character.hxx

Change-Id: I79f4638866daf8952103c8a521db925150e8dcda
Reviewed-on: https://gerrit.libreoffice.org/24709Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Michael Meeks <michael.meeks@collabora.com>