Commit 083735f4 ("rds: switch rds_message_copy_from_user() to iov_iter")
breaks rds_message_copy_from_user() semantics on success, and causes it
to return nbytes copied, when it should return 0.  This commit fixes that bug.
Signed-off-by: NSowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>