docs: Fix attribute names in filesystem/driver example

Signed-off-by: NJim Fehlig <jfehlig@suse.com>

docs/formatdomain.html.in

@@ -3847,7 +3847,7 @@
     <readonly/>
   </filesystem>
   <filesystem type='file' accessmode='passthrough'>
-    <driver name='loop' type='raw'/>
+    <driver type='loop' format='raw'/>
     <driver type='path' wrpolicy='immediate'/>
     <source file='/export/to/guest.img'/>
     <target dir='/import/from/host'/>