NFSv4.1: Clear lseg pointer in ->doio function

Now that we have access to the pointer, clear it immediately after
the put, instead of in caller.

Signed-off-by: Fred Isaman <iisaman@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

diff --cc fs/nfs/pagelist.c
Simple merge

diff --cc fs/nfs/read.c
Simple merge

diff --cc fs/nfs/write.c
Simple merge