pNFS: Fix RCU lock leakage

Another brown paper bag moment. pnfs_alloc_ds_commits_list() is leaking
the RCU lock.

Fixes: a9901899 ("pNFS: Add infrastructure for cleaning up per-layout commit structures")
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/pnfs_nfs.c

@@ -501,6 +501,7 @@ pnfs_alloc_ds_commits_list(struct list_head *list,
 		rcu_read_lock();
 		pnfs_put_commit_array(array, cinfo->inode);
 	}
+	rcu_read_unlock();
 	return ret;
 }