virHashAddOrUpdateEntry: Turn @new_name into void *

virHashAddOrUpdateEntry: Turn @new_name into void *

In 9190f0b0 we've tried to fix an OOM. And boy, was that fix
successful. But back then, the hash table implementation worked
strictly over string keys, which is not the case anymore. Hash
table have this function keyCopy() which returns void *.
Therefore a local variable that is temporarily holding the
intermediate return value from that function should be void *
too.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>