Currently, it's just an additional check. But later this will be used
int the following way. Return value "1" means, that fle is not ready
for restore, and the caller should recall this method once again later.
See "[PATCH] files: Kill struct file_desc_ops::post_open" for the details.

v5: Use "1" for return

v2: Use generic FLE_OPEN and FLE_RESTORED to determ if a fle is ready
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>