doc: Fix reference to #elementsUSB

aae0fc2a removed the #elementsUSB anchor
but did not update the links to point to the new section #elementsHostDev.
Signed-off-by: NPhilipp Hahn <hahn@univention.de>

docs/formatdomain.html.in

@@ -146,7 +146,7 @@
         configure in the desired way, which is why per-device boot elements
         (see <a href="#elementsDisks">disks</a>,
         <a href="#elementsNICS">network interfaces</a>, and
-        <a href="#elementsUSB">USB and PCI devices</a> sections below) were
+        <a href="#elementsHostDev">USB and PCI devices</a> sections below) were
         introduced and they are the preferred way providing full control over
         booting order. The <code>boot</code> element and per-device boot
         elements are mutually exclusive. <span class="since">Since 0.1.3,

docs/formatnode.html.in

@@ -13,7 +13,7 @@
       prefix <code>virNodeDevice</code>, which deal with management of
       host devices that can be handed to guests via passthrough as
       &lt;hostdev&gt; elements
-      in <a href="formatdomain.html#elementsUSB">the domain XML</a>.
+      in <a href="formatdomain.html#elementsHostDev">the domain XML</a>.
       These devices are represented as a hierarchy, where a device on
       a bus has a parent of the bus controller device; the root of the
       hierarchy is the node named "computer".