package/dvblast: always needs iconv

dvblast wants iconv functions even without locales.

Fixes:
    http://autobuild.buildroot.org/results/03f/03fe6dc17d7f36d9b8c7ced402850def95d8feb3/
    http://autobuild.buildroot.org/results/064/0647b0180ac9a6bf6172742e388df9a9e584d91b/


    ...

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Julian Scheel <julian@jusst.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>