scsi: megaraid_sas: 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/20210329094532.4165147-1-liushixin2@huawei.com
Acked-by: Sumit Saxena <sumit.saxena@broadcom.com>
Signed-off-by: Shixin Liu <liushixin2@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>