docs: Change the 'Launch Security' section id to "launchSecurity"

Although there's currently only support for SEV, it's likely other
solutions will appear, so we should not refer to the documentation
section simply with 'sev'.
Signed-off-by: NErik Skultety <eskultet@redhat.com>

docs/formatdomain.html.in

@@ -8924,7 +8924,7 @@ qemu-kvm -net nic,model=? /dev/null
 
     <p>Note: DEA/TDEA is synonymous with DES/TDES.</p>
 
-    <h3><a id="sev">Launch Security</a></h3>
+    <h3><a id="launchSecurity">Launch Security</a></h3>
 
     <p>
        The contents of the <code>&lt;launchSecurity type='sev'&gt;</code> element