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/dump/create_pel.cpp b/dump/create_pel.cpp
index 07cd07a..f1b6b4b 100644
--- a/dump/create_pel.cpp
+++ b/dump/create_pel.cpp
@@ -179,8 +179,8 @@
         method.append(opEntryInterface);
         method.append("PlatformLogID");
         auto response = bus.call(method);
-        std::variant<uint32_t, std::string> v;
-        response.read(v);
+        auto v = response.unpack<std::variant<uint32_t, std::string>>();
+
         pelId = std::get<uint32_t>(v);
         method =
             bus.new_method_call(service.c_str(), loggingEntryObjectPath.c_str(),
diff --git a/dump/dump_utils.cpp b/dump/dump_utils.cpp
index 74ec563..fa776a6 100644
--- a/dump/dump_utils.cpp
+++ b/dump/dump_utils.cpp
@@ -87,8 +87,7 @@
                  uint64_t(failingUnit)}};
 
         method.append(createParams);
-        sdbusplus::message::object_path reply;
-        bus.call(method).read(reply);
+        auto reply = bus.call(method).unpack<sdbusplus::message::object_path>();
 
         monitorDumpCreation(reply.str, SBE_DUMP_TIMEOUT);
     }
@@ -131,8 +130,9 @@
         mapper.append(path, std::vector<std::string>({intf}));
 
         auto mapperResponseMsg = bus.call(mapper);
-        std::map<std::string, std::vector<std::string>> mapperResponse;
-        mapperResponseMsg.read(mapperResponse);
+        auto mapperResponse =
+            mapperResponseMsg
+                .unpack<std::map<std::string, std::vector<std::string>>>();
 
         if (mapperResponse.empty())
         {