softoff: fix use of deprecated sdbusplus type

sdbusplus removed the `phosphor` namespace alias to `sdbusplus::Timer`.
Fix here to use the original type.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I73772df569aa6efb20e3647b205b8db55220a1f3
diff --git a/softoff/softoff.hpp b/softoff/softoff.hpp
index d525d11..14742e1 100644
--- a/softoff/softoff.hpp
+++ b/softoff/softoff.hpp
@@ -102,7 +102,7 @@
     sdbusplus::bus_t& bus;
 
     /** @brief Reference to Timer object */
-    Timer timer;
+    sdbusplus::Timer timer;
 
     /** @brief Marks the end of life of this application.
      *