qemu_agent: Resolve Coverity RESOURCE_LEAK

Coverity found that on error paths, the 'arg' value wasn't be cleaned
up. Followed the example in qemuAgentSetVCPUs() where upon successful call
to qemuAgentCommand() the 'cpus' is set to NULL; otherwise, when cleanup
occurs the free the memory for 'arg'

src/qemu/qemu_agent.c

@@ -1328,7 +1328,7 @@ int qemuAgentFSFreeze(qemuAgentPtr mon, const char **mountpoints,
                       unsigned int nmountpoints)
 {
     int ret = -1;
-    virJSONValuePtr cmd, arg;
+    virJSONValuePtr cmd, arg = NULL;
     virJSONValuePtr reply = NULL;
 
     if (mountpoints && nmountpoints) {
@@ -1343,7 +1343,8 @@ int qemuAgentFSFreeze(qemuAgentPtr mon, const char **mountpoints,
     }
 
     if (!cmd)
-        return -1;
+        goto cleanup;
+    arg = NULL;
 
     if (qemuAgentCommand(mon, cmd, &reply, true,
                          VIR_DOMAIN_QEMU_AGENT_COMMAND_BLOCK) < 0)
@@ -1355,6 +1356,7 @@ int qemuAgentFSFreeze(qemuAgentPtr mon, const char **mountpoints,
     }
 
  cleanup:
+    virJSONValueFree(arg);
     virJSONValueFree(cmd);
     virJSONValueFree(reply);
     return ret;