Each string which is shown during readline completion in the QEMU monitor
is allocated dynamically but currently never deallocated.

Add the missing loop which calls g_free for the allocated strings.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Reviewed-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>