nfscl: Add a missing delegation lock release

There was a case in nfscl_doiods() where the function would return
without releasing the delegation shared lock, if it was aquired by
the call to nfscl_getstateid(). This patch adds that release.

I have never observed a failure due to this missing release, so I
do not know if it ever happens in practice. However, since the pNFS
client is not yet heavily used, it might be the case.

Found by code inspection during a recent NFSv4 IETF working group
testing event.

MFC after: 2 week