lan743x: Make symbol lan743x_pm_ops static

Fixes the following sparse warning:

drivers/net/ethernet/microchip/lan743x_main.c:2944:25: warning:
 symbol 'lan743x_pm_ops' was not declared. Should it be static?

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Bryan Whitehead <Bryan.Whitehead@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>