cppcheck: Make settings constructor explicit

This change fixes this cppcheck warning:
Struct 'Objects' has a constructor with 1 argument that is not explicit.

Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
Change-Id: I6bcb550626dd6b2de4b0dd44592e4ac0050ab22d
diff --git a/settings.hpp b/settings.hpp
index a1a9a6e..7571fe1 100644
--- a/settings.hpp
+++ b/settings.hpp
@@ -25,7 +25,7 @@
      *
      * @param[in] bus - The Dbus bus object
      */
-    Objects(sdbusplus::bus::bus& bus);
+    explicit Objects(sdbusplus::bus::bus& bus);
     Objects(const Objects&) = delete;
     Objects& operator=(const Objects&) = delete;
     Objects(Objects&&) = delete;