native: don't call steal_pointer prematurely

commit e2bfaf07 does this:

g_hash_table_insert (cards,
                     g_udev_device_get_name (parent_device),
                     g_steal_pointer (&parent_device));

The problem is the g_steal_pointer call may happen before the
g_udev_device_get_name call leading to a crash.

This commit does the get_name call on an earlier line

https://bugzilla.gnome.org/show_bug.cgi?id=771442