Stop using mapbox directly

This is going to be removed from sdbusplus

Change-Id: I912f560fac7d41e13d3754df9363b95cedac78f8
Signed-off-by: Yoo, Jae Hyun <jae.hyun.yoo@intel.com>
diff --git a/sensors/src/ADCSensorMain.cpp b/sensors/src/ADCSensorMain.cpp
index 845b976..47edd5c 100644
--- a/sensors/src/ADCSensorMain.cpp
+++ b/sensors/src/ADCSensorMain.cpp
@@ -29,6 +29,7 @@
 static constexpr bool DEBUG = false;
 
 namespace fs = std::experimental::filesystem;
+namespace variant_ns = sdbusplus::message::variant_ns;
 static constexpr std::array<const char*, 1> SENSOR_TYPES = {
     "xyz.openbmc_project.Configuration.ADC"};
 static std::regex INPUT_REGEX(R"(in(\d+)_input)");
@@ -177,8 +178,8 @@
         float scaleFactor = 1.0;
         if (findScaleFactor != baseConfiguration->second.end())
         {
-            scaleFactor = mapbox::util::apply_visitor(VariantToFloatVisitor(),
-                                                      findScaleFactor->second);
+            scaleFactor = variant_ns::visit(VariantToFloatVisitor(),
+                                            findScaleFactor->second);
         }
         sensors[sensorName] = std::make_unique<ADCSensor>(
             path.string(), objectServer, dbusConnection, io, sensorName,