package/gerbera: fix static linking with libmagic

This patch was wrongly removed when bumping the version to 1.4.0 in
commit 6976f312

Fixes:
 - http://autobuild.buildroot.org/results/7a53a59dd08c043f371bea967c3b450a7bddcde8



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>