util: fix improper assignment of return value in virHostdevReadNetConfig()

Commit 9a94af6d restructured virHostdevReadNetConfig() so that it
would manually set ret = 0 after successfully reading the device's
config, but Coverity pointed out that "ret = 0" was erroneously placed
outside of an "else" clause, meaning that the the value of ret set in
the "if" clause was unnecessarily and incorrectly overwritten.

This patch moves ret = 0 into the else clause, which should silence
Coverity.

src/util/virhostdev.c

@@ -641,9 +641,9 @@ virHostdevRestoreNetConfig(virDomainHostdevDefPtr hostdev,
 
         ignore_value(virNetDevSetNetConfig(linkdev, vf,
                                            adminMAC, vlan, MAC, true));
+        ret = 0;
     }
 
-    ret = 0;
  cleanup:
     VIR_FREE(linkdev);
     VIR_FREE(MAC);