pldm: Fix calling getProperty method in GetDateTime method

An error in calling the getProperty method in the GetDateTime method
resulted in GetDateTime always returns epoch time 0.

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: Iecdbbc489c298a2544d72599110116b7f4373857
diff --git a/libpldmresponder/bios.cpp b/libpldmresponder/bios.cpp
index 13b36ab..2d3a8ee 100644
--- a/libpldmresponder/bios.cpp
+++ b/libpldmresponder/bios.cpp
@@ -145,13 +145,12 @@
     constexpr auto hostTimePath = "/xyz/openbmc_project/time/host";
     Response response(sizeof(pldm_msg_hdr) + PLDM_GET_DATE_TIME_RESP_BYTES, 0);
     auto responsePtr = reinterpret_cast<pldm_msg*>(response.data());
-    std::variant<EpochTimeUS> value;
+    EpochTimeUS timeUsec;
 
     try
     {
-        value = pldm::utils::DBusHandler()
-                    .getDbusProperty<std::variant<EpochTimeUS>>(
-                        hostTimePath, "Elapsed", timeInterface);
+        timeUsec = pldm::utils::DBusHandler().getDbusProperty<EpochTimeUS>(
+            hostTimePath, "Elapsed", timeInterface);
     }
     catch (const sdbusplus::exception::SdBusError& e)
     {
@@ -164,8 +163,6 @@
         return response;
     }
 
-    uint64_t timeUsec = std::get<EpochTimeUS>(value);
-
     uint64_t timeSec = std::chrono::duration_cast<std::chrono::seconds>(
                            std::chrono::microseconds(timeUsec))
                            .count();