docs: Fix a typo in formatdomain.html

Signed-off-by: NHan Han <hhan@redhat.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>

docs/formatdomain.html.in

@@ -7039,7 +7039,7 @@ qemu-kvm -net nic,model=? /dev/null
   <input type='keyboard' bus='virtio'/>
   <input type='tablet' bus='virtio'/>
   <input type='passthrough' bus='virtio'>
-    <source evdev='/dev/input/event1/>
+    <source evdev='/dev/input/event1'/>
   </input>
 </devices>
 ...</pre>