Clock applet help: Fix speed unit for meters per second

Author: rbuj

help/mate-clock/C/index.docbook

@@ -469,7 +469,7 @@ The <application>&applet;</application> applet displays the date and time, and w
 			 <para><guilabel>km/h</guilabel> (kilometers per hour)</para>
 			</listitem>
 			 <listitem>
-			 <para><guilabel>Dm/a</guilabel> (meters per second)</para>
+			 <para><guilabel>m/s</guilabel> (meters per second)</para>
 			</listitem>
 			 <listitem>
 			 <para><guilabel>Default</guilabel> The default display for your region.</para>