docs: formatdomain: use 'element' instead of 'block'

Signed-off-by: NJán Tomko <jtomko@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>

docs/formatdomain.html.in

@@ -3979,7 +3979,7 @@
           <span class="since"> (since 0.9.13)</span></dd>
         </dl>
 
-      The filesystem block has an optional attribute <code>accessmode</code>
+      The filesystem element has an optional attribute <code>accessmode</code>
       which specifies the security mode for accessing the source
       <span class="since">(since 0.8.5)</span>. Currently this only works
       with <code>type='mount'</code> for the QEMU/KVM driver. The possible