NFSv4.x: Fix handling of partially delegated locks

If a NFS client receives a delegation for a file after it has taken
a lock on that file, we can currently end up in a situation where
we mistakenly skip unlocking that file.

The following patch swaps an erroneous check in nfs4_proc_unlck for
whether or not the file has a delegation to one which checks whether
or not we hold a lock stateid for that file.

Reported-by: Chuck Lever <Chuck.Lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@vger.kernel.org [>=3.7]
Tested-by: Chuck Lever <Chuck.Lever@oracle.com>