dmaengine: Freescale: use spin_lock_bh instead of spin_lock_irqsave

The usage of spin_lock_irqsave() is a stronger locking mechanism than is
required throughout the driver. The minimum locking required should be used
instead. Interrupts will be turned off and context will be saved, it is
unnecessary to use irqsave.

This patch changes all instances of spin_lock_irqsave() to spin_lock_bh(). All
manipulation of protected fields is done using tasklet context or weaker, which
makes spin_lock_bh() the correct choice.

Signed-off-by: Hongbo Zhang <hongbo.zhang@freescale.com>
Signed-off-by: Qiang Liu <qiang.liu@freescale.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>