net: ethernet: litex: Remove unnecessary print function dev_err()

The print function dev_err() is redundant because
platform_get_irq() already prints an error.

Signed-off-by: Xu Wang <vulab@iscas.ac.cn>
Reviewed-by: Cai Huoqing <caihuoqing@baidu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>