cups-filters: Add patch to remove relative symbolic link from install

cups-filters: Add patch to remove relative symbolic link from install

On older build systems with old coreutils, using relative symbolic link
(ln -r) does not work, and causes failed builds. Workaround is to use
normal symbolic link with a relative path. e.g. ../../$(BINDIR)

This fix is dependent on bumping cups-filters version to 1.20.1 because
of autotools issue with Makefile.am changes.

Fixes:
http://autobuild.buildroot.net/results/77a6369f3530a2a6a055f7fd664f1ad424274d77

Signed-off-by: Olivier Schonken <olivier.schonken@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>