dma: ipu: Drop unused spinlock

I was checking why this spinlock was never initialized, but it turns
out it's not used anywhere, so we can drop it.

Signed-off-by: Jean Delvare <[e-mail]>
Cc: Vinod Koul <[e-mail]>
Signed-off-by: Dan Williams <[e-mail]>

drivers/dma/ipu/ipu_irq.c

···
 struct ipu_irq_bank {
 	unsigned int	control;
 	unsigned int	status;
-	spinlock_t	lock;
 	struct ipu	*ipu;
 };