net: ethernet: ti: am65-cpsw: handle deferred probe with dev_err_probe()

Use new dev_err_probe() API to handle deferred probe properly and simplify
the code.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>