nfsd4: fix state lock usage in LOCKU

nfsd4: fix state lock usage in LOCKU

In commit 5ec094c1096ab3bb795651855d53f18daa26afde "nfsd4: extend state
lock over seqid replay logic" I modified the exit logic of all the
seqid-based procedures except nfsd4_locku().  Fix the oversight.

The result of the bug was a double-unlock while handling the LOCKU
procedure, and a warning like:

[  142.150014] WARNING: at kernel/mutex-debug.c:78 debug_mutex_unlock+0xda/0xe0()
...
[  142.152927] Pid: 742, comm: nfsd Not tainted 3.1.0-rc1-SLIM+ #9
[  142.152927] Call Trace:
[  142.152927]  [<ffffffff8105fa4f>] warn_slowpath_common+0x7f/0xc0
[  142.152927]  [<ffffffff8105faaa>] warn_slowpath_null+0x1a/0x20
[  142.152927]  [<ffffffff810960ca>] debug_mutex_unlock+0xda/0xe0
[  142.152927]  [<ffffffff813e4200>] __mutex_unlock_slowpath+0x80/0x140
[  142.152927]  [<ffffffff813e42ce>] mutex_unlock+0xe/0x10
[  142.152927]  [<ffffffffa03bd3f5>] nfs4_lock_state+0x35/0x40 [nfsd]
[  142.152927]  [<ffffffffa03b0b71>] nfsd4_proc_compound+0x2a1/0x690
[nfsd]
[  142.152927]  [<ffffffffa039f9fb>] nfsd_dispatch+0xeb/0x230 [nfsd]
[  142.152927]  [<ffffffffa02b1055>] svc_process_common+0x345/0x690
[sunrpc]
[  142.152927]  [<ffffffff81058d10>] ? try_to_wake_up+0x280/0x280
[  142.152927]  [<ffffffffa02b16e2>] svc_process+0x102/0x150 [sunrpc]
[  142.152927]  [<ffffffffa039f0bd>] nfsd+0xbd/0x160 [nfsd]
[  142.152927]  [<ffffffffa039f000>] ? 0xffffffffa039efff
[  142.152927]  [<ffffffff8108230c>] kthread+0x8c/0xa0
[  142.152927]  [<ffffffff813e8694>] kernel_thread_helper+0x4/0x10
[  142.152927]  [<ffffffff81082280>] ? kthread_worker_fn+0x190/0x190
[  142.152927]  [<ffffffff813e8690>] ? gs_change+0x13/0x13

Reported-by: Bryan Schumaker <bjschuma@netapp.com>
Tested-by: Bryan Schumaker <bjschuma@netapp.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>