NFSv4: Clean up the error handling for nfs4_reclaim_lease

Try to consolidate the error handling for nfs4_reclaim_lease into
a single function instead of doing a bit here, and a bit there...

Also ensure that NFS4CLNT_PURGE_STATE handles errors correctly.

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