use sdbusplus unpack syntax

Rather than defining a variable and then reading it from a message,
sdbusplus also supports directly unpack-ing from the message.  Use
this syntax instead as it is more efficient and succinct.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I311c0a4a3aa8b68ea2814c00eaff11e2e8803fb1
diff --git a/watchdog/watchdog_handler.cpp b/watchdog/watchdog_handler.cpp
index 5f48ac5..169be42 100644
--- a/watchdog/watchdog_handler.cpp
+++ b/watchdog/watchdog_handler.cpp
@@ -157,8 +157,7 @@
             auto response = bus.call(method);
 
             // reply will be type dbus::ObjectPath
-            sdbusplus::message::object_path reply;
-            response.read(reply);
+            auto reply = response.unpack<sdbusplus::message::object_path>();
 
             // monitor dump progress
             monitorDump(reply, dumpParameters.timeout);