dmaengine: rcar-dmac: Fix spinlock issues in interrupt

The rcar_dmac_desc_put() function is called in interrupt context and
must thus use spin_lock_irqsave() instead of spin_lock_irq().

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>