Revert r30869 "Remove buildserver_modelname value."

The buildserver_modelname is still in use, and the commit missed some parts on
removal, causing segfaults on start.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@30884 a1c6a512-1295-4272-9138-f99709370657

rbutil/rbutilqt/base/systeminfo.cpp

@@ -57,6 +57,7 @@ const static struct {
     { SystemInfo::CurEncoder,           ":platform:/encoder",   "" },
     { SystemInfo::CurBrand,             ":platform:/brand",     "" },
     { SystemInfo::CurName,              ":platform:/name",      "" },
+    { SystemInfo::CurBuildserverModel,  ":platform:/buildserver_modelname", "" },
     { SystemInfo::CurConfigureModel,    ":platform:/configure_modelname", "" },
 };