Convert variant usage to std interface

This is just a refactoring to use the c++17 std::variant interfaces
instead of the mapbox::variant specific ones. We should be able to use
mapbox::variant and std::variant interchangeably now.

Tested:
    Built against sdbusplus with mapbox::variant and sbusplus using
    std::variant. Both variant compile and test out.

Change-Id: I6fbaad3d12dd34968db6a10f3d74a65e07d0f0cc
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/settings.cpp b/settings.cpp
index 770bde0..0ddd7a6 100644
--- a/settings.cpp
+++ b/settings.cpp
@@ -4,6 +4,7 @@
 
 #include <phosphor-logging/elog-errors.hpp>
 #include <phosphor-logging/log.hpp>
+#include <sdbusplus/message/types.hpp>
 #include <xyz/openbmc_project/Common/error.hpp>
 
 namespace settings
@@ -11,6 +12,7 @@
 
 using namespace phosphor::logging;
 using namespace sdbusplus::xyz::openbmc_project::Common::Error;
+namespace variant_ns = sdbusplus::message::variant_ns;
 
 constexpr auto mapperService = "xyz.openbmc_project.ObjectMapper";
 constexpr auto mapperPath = "/xyz/openbmc_project/object_mapper";
@@ -131,7 +133,7 @@
 
     sdbusplus::message::variant<bool> enabled;
     reply.read(enabled);
-    auto oneTimeEnabled = enabled.get<bool>();
+    auto oneTimeEnabled = variant_ns::get<bool>(enabled);
     const Path& setting = oneTimeEnabled ? oneTimeSetting : regularSetting;
     return std::make_tuple(setting, oneTimeEnabled);
 }