net: encx24j600: make encx24j600_hw_init() return void

This function always return 0 now, we can make it return void to
simplify the code. This fixes the following coccicheck warning:

drivers/net/ethernet/microchip/encx24j600.c:609:5-8: Unneeded variable:
"ret". Return "0" on line 653

Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>