udp\udp_callback.c: Fix another C89 compatibility problem. Empty initializers are not permitted. Caused ez80 build failure.

fs/vfs/fs_poll.c

@@ -128,7 +128,8 @@ static int poll_fdsetup(int fd, FAR struct pollfd *fds, bool setup)
  *
  ****************************************************************************/
 
-static inline int poll_setup(FAR struct pollfd *fds, nfds_t nfds, sem_t *sem)
+static inline int poll_setup(FAR struct pollfd *fds, nfds_t nfds,
+                             FAR sem_t *sem)
 {
   unsigned int i;
   unsigned int j;

net/udp/udp_callback.c

@@ -84,11 +84,13 @@ static uint16_t udp_datahandler(FAR struct net_driver_s *dev, FAR struct udp_con
 #ifdef CONFIG_NET_IPv6
   FAR struct sockaddr_in6 src_addr6 =
   {
+    0
   };
 #endif
 #ifdef CONFIG_NET_IPv4
   FAR struct sockaddr_in src_addr4 =
   {
+    0
   };
 #endif
   FAR void  *src_addr;