fuse: set stolen page uptodate

[ Upstream commit aa991b3b ]

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>
Cc: stable@vger.kernel.org
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>