net: phy: Make iproc_mdio_resume static

Fix sparse warnings:

drivers/net/phy/mdio-bcm-iproc.c:182:5: warning:
 symbol 'iproc_mdio_resume' was not declared. Should it be static?

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>