mtip32xx: Use plain spinlock for 'cmd_issue_lock'

'cmd_issue_lock' is for only acquiring a free slot, and it is not used
in interrupt context. So replaced irq version with non-irq version of spinlock.

Signed-off-by: Asai Thambi S P <asamymuthupa@micron.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>