package/nut: fix parallel install

Fixes:
    http://autobuild.buildroot.net/results/256/2567e13cd5bc702bc3a38a1d6fc8e34022cc7db5/



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