commit aa991b3b upstream.

Regular pipe buffers' ->steal method (generic_pipe_buf_steal()) doesn't set
PG_uptodate.

Don't warn on this condition, just set the uptodate flag.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>