net: stmmac: dwc-qos: Change the dwc_eth_dwmac_data's .probe prototype

The return pointer of dwc_eth_dwmac_data's .probe isn't used, and
"probe" usually return int, so change the prototype to follow standard
way. Secondly, it can simplify the tegra_eqos_probe() code.

Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Link: https://lore.kernel.org/r/20201109160440.3a736ee3@xhacker.debian
Signed-off-by: Jakub Kicinski <kuba@kernel.org>