fold security_file_free() into file_free()

.. and the call of file_free() in case of security_file_alloc() failure
in get_empty_filp() should be simply file_free_rcu() - no point in
rcu-delays there, anyway.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>