Flash filesystems: Fix a typo

Remove a redundant verb.

Signed-off-by: Nasser Afshin <afshin.nasser@gmail.com>
Reviewed-by: Michael Opdenacker <michael.opdenacker@bootlin.com>

slides/sysdev-flash-filesystems/sysdev-flash-filesystems.tex

@@ -841,7 +841,7 @@ \section{Flash storage and filesystems}
   \begin{itemize}
     \item \code{ubiformat} and \code{ubinfo} are not implemented yet
     \item \code{ubirsvol} doesn't support \code{-N <name>}. You have
-      to use specify the volume to resize by its id (\code{-n num}):\\
+      to specify the volume to resize by its id (\code{-n num}):\\
       \code{ubirsvol /dev/ubi0 -n 4 -s 64 MiB}
     \end{itemize}
 \end{frame}