fix producer reference

Author: Vladimir Kotal

proc.tex

@@ -951,7 +951,7 @@
 \item Closing the writing descriptor \texttt{pd[1]} (see
 ifdef([[[NOSPELLCHECK]]], [[[{\color[rgb]{1,0,0} $\triangleright$}]]]))
 in the consumer process is required as the EOF would not be detected otherwise.
-\item Closing the reading descriptor \texttt{pd[0]} in the consumer process is
+\item Closing the reading descriptor \texttt{pd[0]} in the producer process is
 desired as well (see
 ifdef([[[NOSPELLCHECK]]], [[[{\color[rgb]{1,0,0} $\triangleright$}]]])
 ) as if the consumer finishes prematurely the producer properly gets a