dmaengine: altera: fix spinlock usage

Since this lock is acquired in both process and IRQ context, failing to
to disable IRQs when trying to acquire the lock in process context can
lead to deadlocks.

Signed-off-by: Sylvain Lesne <lesne@alse-fr.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>