wifi-dialog: fix wrong free

Fixes: 755cc564

#43
7 jobs for master in 13 minutes and 1 second (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #219335
fedora28_dist

00:07:11

 
  Test
passed #219339
fedora_autotools_full

00:02:46

passed #219338
fedora_autotools_minimal

00:02:37

passed #219337
fedora_meson_full

00:02:56

passed #219336
fedora_meson_minimal

00:02:28

 
  Deploy
passed #219340
pages

00:02:52

passed pages:deploy

00:00:00