ceph: no need to invalidate the fscache twice

Fixes: 400e1286 ("ceph: conversion to new fscache API")
Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>