net: ethernet: davinci_emac: make local function emac_poll_controller() static

emac_poll_controller() was not declared. It should be static.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>