net: phy: bcm54140: Make a bunch of functions static

Fix the following warning:

drivers/net/phy/bcm54140.c:663:5: warning:
symbol 'bcm54140_did_interrupt' was not declared. Should it be static?
drivers/net/phy/bcm54140.c:672:5: warning:
symbol 'bcm54140_ack_intr' was not declared. Should it be static?
drivers/net/phy/bcm54140.c:684:5: warning:
symbol 'bcm54140_config_intr' was not declared. Should it be static?

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: ChenTao <chentao107@huawei.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>