fsnotify: Fix nil dereference in pre_dump_one_fanotify

pre_dump_one_fanotify calls for parse_fdinfo_pid_s where
fsn_params mut not be NULL, otherwise we get nil dereference.

Fix it by passing a real variable instead.

Reported-by: Pavel Tikhomirov <snorcht@gmail.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>