NFSv4: Fix an Oops in nfs4_free_lock_state

The oops http://www.kerneloops.org/raw.php?rawid=537858&msgid= appears to
be due to the nfs4_lock_state->ls_state field being uninitialised. This
happens if the call to nfs4_free_lock_state() is triggered at the end of
nfs4_get_lock_state().

The fix is to move the initialisation of ls_state into the allocator.

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