net: qcom/emac: Find sgmii_ops by device_for_each_child()

net: qcom/emac: Find sgmii_ops by device_for_each_child()

To prepare for constifying the following old driver core API:

struct device *device_find_child(struct device *dev, void *data,
		int (*match)(struct device *dev, void *data));
to new:
struct device *device_find_child(struct device *dev, const void *data,
		int (*match)(struct device *dev, const void *data));

The new API does not allow its match function (*match)() to modify
caller's match data @*data, but emac_sgmii_acpi_match(), as the old
API's match function, indeed modifies relevant match data, so it is
not suitable for the new API any more, solved by implementing the same
finding sgmii_ops function by correcting the function and using it
as parameter of device_for_each_child() instead of device_find_child().

By the way, this commit does not change any existing logic.

Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
Link: https://patch.msgid.link/20241003-qcom_emac_fix-v6-1-0658e3792ca4@quicinc.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>