net: macb: simplify error paths in init_reset_optional()

The error handling paths in init_reset_optional() can all be
simplified to return dev_err_probe(). Do so.

Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>