package/libvirt: fix libvirtd option

Replace libvirtd by driver_libvirtd to avoid the following build failure
raised since the addition of the package in commit
ccfc90e1:

../output-1/build/libvirt-7.7.0/meson.build:1:0: ERROR: Unknown options: "libvirtd"

Fixes:
 - http://autobuild.buildroot.org/results/3a20db6cb39c0d91213adbe82934274659df43e7



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>