package/libdvdread: needs host-pkgconf

Add host-pkgconf to the dependencies since pkg-config is used to find
libdvdcss.

Fixes:
http://autobuild.buildroot.net/results/e5f/e5fffdd51bdd6962149a836af1e7a6bbc6bae20c



Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>