sdbusplus: remove deprecated variant_ns

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: If06a676c19b2005c388a6ac48ba2d9f13e7615b2
diff --git a/control/zone.hpp b/control/zone.hpp
index 8415def..71fba32 100644
--- a/control/zone.hpp
+++ b/control/zone.hpp
@@ -202,7 +202,7 @@
                                      const std::string& interface,
                                      const std::string& property)
         {
-            return sdbusplus::message::variant_ns::get<T>(
+            return std::get<T>(
                     _properties.at(object).at(interface).at(property));
         };