nfsd: fix comments on nfsd_cache_lookup

/*

 * Try to find an entry matching the current call in the cache. When none

 * is found, we grab the oldest unlocked entry off the LRU list.

 * Note that no operation within the loop may sleep.

 * is found, we try to grab the oldest expired entry off the LRU list. If

 * a suitable one isn't there, then drop the cache_lock and allocate a

 * new one, then search again in case one got inserted while this thread

 * didn't hold the lock.

 */

int

nfsd_cache_lookup(struct svc_rqst *rqstp)

		}

	}

	/* Drop the lock and allocate a new entry */

	spin_unlock(&cache_lock);

	rp = nfsd_reply_cache_alloc();

	if (!rp) {