package/dvb-apps: fix build with kernel headers >= 4.14

Fixes:
    http://autobuild.buildroot.org/results/708/708f11809b2cafc2a3375dc515803c87b376ed4d/
    http://autobuild.buildroot.org/results/6e1/6e161926577355ced82426536227ddd2ba130f06/


    [...]

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