RDMA/iw_cxgb4: Use DEFINE_SPINLOCK() for spinlock

spinlock can be initialized automatically with DEFINE_SPINLOCK() rather
than explicitly calling spin_lock_init().

Link: https://lore.kernel.org/r/20210331020105.4858-1-tangyizhou@huawei.com


Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Tang Yizhou <tangyizhou@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>