net/icmp/icmp_netpoll.c: Fix return of uninitialized 'ret' when no error occurs. That is, on what should be a successful return from this function, an uninitialized value was returned, which may indicate an undeserved error.

net/icmp/icmp_netpoll.c

@@ -159,7 +159,7 @@ int icmp_pollsetup(FAR struct socket *psock, FAR struct pollfd *fds)
   FAR struct icmp_conn_s *conn = psock->s_conn;
   FAR struct icmp_poll_s *info;
   FAR struct devif_callback_s *cb;
-  int ret;
+  int ret = OK;
 
   DEBUGASSERT(conn != NULL && fds != NULL);