dmaengine: edma: No need save/restore interrupt flags during spin_lock in IRQ

The vchan lock in edma_callback is acquired in hard interrupt context. As
interrupts are already disabled, there's no point in save/restoring interrupt
mask bit or cpsr flags.

Get rid of flags local variable and use spin_lock instead of spin_lock_irqsave.

Signed-off-by: Joel Fernandes <joelf@ti.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>