Stop using mapbox namespace directly

sdbusplus is transitioning to std::variant, the
sdbusplus::message::variant_ns will be changed to std
and should move over correctly, but mapbox will be deleted.

Tested-by: It built

Change-Id: I25672cef16a6c75ae2f3619d319ade1eb063a98b
Signed-off-by: James Feist <james.feist@linux.intel.com>
diff --git a/dbus/dbuspassive.cpp b/dbus/dbuspassive.cpp
index e269b3d..702bf8d 100644
--- a/dbus/dbuspassive.cpp
+++ b/dbus/dbuspassive.cpp
@@ -99,8 +99,8 @@
         auto valPropMap = msgData.find("Value");
         if (valPropMap != msgData.end())
         {
-            double value = mapbox::util::apply_visitor(VariantToDoubleVisitor(),
-                                                       valPropMap->second);
+            double value = sdbusplus::message::variant_ns::apply_visitor(
+                VariantToDoubleVisitor(), valPropMap->second);
 
             value *= std::pow(10, owner->getScale());