Add missing `$(DESTDIR)` for `install-data-hook`

The target breaks on systems like Arch Linux, where package building is
done with `DESTDIR`, which is needed because the packaging step is not
allowed to modify files in the actual root system, instead it has to
work in a fakeroot environment.
Merge pull request #1105 from asaaki/makefile-patch

Add missing `$(DESTDIR)` for `install-data-hook`