net: hip04: add missing MODULE_LICENSE

The hip04 ethernet driver causes a new compile-time warning
when built as a loadable module:

WARNING: modpost: missing MODULE_LICENSE() in drivers/net/ethernet/hisilicon/hip04_eth.o
see include/linux/module.h for more information

This adds the license as "GPL", which matches the header of the file.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Ding Tianhong <dingtianhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>