nfsd: simplify put of fi_deleg_file

fi_delegees is basically just a reference count on users of
fi_deleg_file, which is cleared when fi_delegees goes to zero.  The
fi_deleg_file check here is redundant.  Also add an assertion to make
sure we don't have unbalanced puts.
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>

fs/nfsd/nfs4state.c

@@ -879,9 +879,12 @@ static void nfs4_put_deleg_lease(struct nfs4_file *fp)
 {
 	struct file *filp = NULL;
 
+	WARN_ON_ONCE(!fp->fi_delegees);
+
 	spin_lock(&fp->fi_lock);
-	if (fp->fi_deleg_file && --fp->fi_delegees == 0)
+	if (--fp->fi_delegees == 0) {
 		swap(filp, fp->fi_deleg_file);
+	}
 	spin_unlock(&fp->fi_lock);
 
 	if (filp) {