[PATCH] NFS: Fix Oops in rpc_call_sync()

Fix the Oops in http://bugzilla.linux-nfs.org/show_bug.cgi?id=138


We shouldn't be calling rpc_release_task() for tasks that are not active.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>