Correct invalid reference.

chapters/synchronous.tex

@@ -564,7 +564,7 @@ \subsection{Base-Clock Conversion Operators}\label{base-clock-conversion-operato
 \hline
 \hline
 {\lstinline!sample($u$, $\mathit{clock}$)!} & Sample continuous-time expression & \Cref{modelica:clocked-sample} \\
-{\lstinline!hold($u$)!} & Zeroth order hold of clocked-time variable & \Cref{modelica:clocked-sample} \\
+{\lstinline!hold($u$)!} & Zeroth order hold of clocked-time variable & \Cref{modelica:hold} \\
 \hline
 \end{tabular}
 \end{center}