psu-ng: Use power control constants consistently

To simplify code and promote reuse, use power control constants
consistently.

Signed-off-by: Jim Wright <jlwright@us.ibm.com>
Change-Id: I6eaed534eb48aa06a184848c19c12d6ac7a82518
diff --git a/phosphor-power-supply/psu_manager.cpp b/phosphor-power-supply/psu_manager.cpp
index 320ea55..7654675 100644
--- a/phosphor-power-supply/psu_manager.cpp
+++ b/phosphor-power-supply/psu_manager.cpp
@@ -95,7 +95,7 @@
                                powerService, bus, pgood);
 
         // state is the latest requested power on / off transition
-        auto method = bus.new_method_call(POWER_IFACE, POWER_OBJ_PATH,
+        auto method = bus.new_method_call(powerService.c_str(), POWER_OBJ_PATH,
                                           POWER_IFACE, "getPowerState");
         auto reply = bus.call(method);
         int state = 0;
@@ -478,16 +478,13 @@
 void PSUManager::setPowerSupplyError(const std::string& psuErrorString)
 {
     using namespace sdbusplus::xyz::openbmc_project;
-    constexpr auto service = "org.openbmc.control.Power";
-    constexpr auto objPath = "/org/openbmc/control/power0";
-    constexpr auto interface = "org.openbmc.control.Power";
     constexpr auto method = "setPowerSupplyError";
 
     try
     {
         // Call D-Bus method to inform pseq of PSU error
-        auto methodMsg =
-            bus.new_method_call(service, objPath, interface, method);
+        auto methodMsg = bus.new_method_call(
+            powerService.c_str(), POWER_OBJ_PATH, POWER_IFACE, method);
         methodMsg.append(psuErrorString);
         auto callReply = bus.call(methodMsg);
     }