net: stmmac: Fix missing spin_lock_init in visconti_eth_dwmac_probe()

The driver allocates the spinlock but not initialize it.
Use spin_lock_init() on it to initialize it correctly.

Fixes: b38dd98f ("net: stmmac: Add Toshiba Visconti SoCs glue driver")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>
Link: https://lore.kernel.org/r/20210223104803.4047281-1-weiyongjun1@huawei.com


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