eth: sp7021: drop free_netdev() from spl2sw_init_netdev()

It's not necessary to free netdev allocated with devm_alloc_etherdev()
and using free_netdev() leads to double free.

Fixes: fd3040b9

 ("net: ethernet: Add driver for Sunplus SP7021")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Link: https://lore.kernel.org/r/20221109150116.2988194-1-weiyongjun@huaweicloud.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>