fuse: remove redundant calls to fuse_copy_finish() in fuse_notify()

Remove tail calls of fuse_copy_finish(), since it's now done from
fuse_dev_do_write().

No functional change.

Reviewed-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>