user_mgmt: drop c_str() when param is std::string

Do not use c_str() when parameter is std::string.

Caught via cppcheck.

Change-Id: Iad7c1296d8be363df10ccf9278231187d7d29052
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/user_channel/user_mgmt.cpp b/user_channel/user_mgmt.cpp
index 42a1e09..a21da8c 100644
--- a/user_channel/user_mgmt.cpp
+++ b/user_channel/user_mgmt.cpp
@@ -656,8 +656,8 @@
     if (userInfo->userEnabled != enabledState)
     {
         std::string userPath = std::string(userObjBasePath) + "/" + userName;
-        setDbusProperty(bus, getUserServiceName().c_str(), userPath.c_str(),
-                        usersInterface, userEnabledProperty, enabledState);
+        setDbusProperty(bus, getUserServiceName(), userPath, usersInterface,
+                        userEnabledProperty, enabledState);
     }
     return IPMI_CC_OK;
 }
@@ -693,8 +693,8 @@
         privAccess.privilege != userInfo->userPrivAccess[syncIndex].privilege)
     {
         std::string userPath = std::string(userObjBasePath) + "/" + userName;
-        setDbusProperty(bus, getUserServiceName().c_str(), userPath.c_str(),
-                        usersInterface, userPrivProperty, priv);
+        setDbusProperty(bus, getUserServiceName(), userPath, usersInterface,
+                        userPrivProperty, priv);
     }
     userInfo->userPrivAccess[chNum].privilege = privAccess.privilege;