fuse: fix possibly missing fuse_copy_finish() call in fuse_notify()

In case of FUSE_NOTIFY_RESEND and FUSE_NOTIFY_INC_EPOCH fuse_copy_finish()
isn't called.

Fix by always calling fuse_copy_finish() after fuse_notify().  It's a no-op
if called a second time.

Fixes: 760eac73 ("fuse: Introduce a new notification type for resend pending requests")
Fixes: 2396356a ("fuse: add more control over cache invalidation behaviour")
Cc: <stable@vger.kernel.org> # v6.9
Reviewed-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>