mount: Move adding cr-time binfmt_misc to collect_mnt_namespaces()

Binfmt_misc may not exist on NS_ROOT, and exist on NS_OTHER that time.
So, add binfmt_misc only if no one mnt_ns has it.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>