net: core: Correct function name dev_uc_flush() in the kerneldoc

Fix the following W=1 kernel build warning(s):

 net/core/dev_addr_lists.c:732: warning: expecting prototype for dev_uc_flush(). Prototype was for dev_uc_init() instead

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>