net: dsa: realtek: make use of dev_err_cast_probe()

Using dev_err_cast_probe() to simplify the code.

Signed-off-by: Hongbo Li <lihongbo22@huawei.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Link: https://patch.msgid.link/20240828121805.3696631-1-lihongbo22@huawei.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>