time-config: fix compile warning

Unused result from 'system' call.

Change-Id: I4f62e82ce51aaa86730aa45553f55d2241fc66f8
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/time-config.cpp b/time-config.cpp
index 9e70044..e6af708 100644
--- a/time-config.cpp
+++ b/time-config.cpp
@@ -533,11 +533,11 @@
         // TODO : https://github.com/openbmc/phosphor-time-manager/issues/1
         if (ntpChangeOp)
         {
-            system("systemctl restart systemd-timesyncd &");
+            r = system("systemctl restart systemd-timesyncd &");
         }
         else
         {
-            system("systemctl stop systemd-timesyncd &");
+            r = system("systemctl stop systemd-timesyncd &");
         }
     }
     return r;