nfsd: update obselete comment referencing the BKL

It's inode->i_lock that's now taken in setlease and break_lease, instead
of the big kernel lock.
Reviewed-by: NJeff Layton <jlayton@kernel.org>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4state.c

@@ -3945,9 +3945,9 @@ static void nfsd_break_one_deleg(struct nfs4_delegation *dp)
 	/*
 	 * We're assuming the state code never drops its reference
 	 * without first removing the lease.  Since we're in this lease
-	 * callback (and since the lease code is serialized by the kernel
-	 * lock) we know the server hasn't removed the lease yet, we know
-	 * it's safe to take a reference.
+	 * callback (and since the lease code is serialized by the
+	 * i_lock) we know the server hasn't removed the lease yet, and
+	 * we know it's safe to take a reference.
 	 */
 	refcount_inc(&dp->dl_stid.sc_count);
 	nfsd4_run_cb(&dp->dl_recall);