Just return -ENOSPC instead of returning 0 and setting the return rt
extent number to NULLRTEXTNO.  This is turn removes all users of
NULLRTEXTNO, so remove that as well.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>