dmaengine: at_hdmac: remove unused function

commit 54f8d501e8 ('dmaengine: remove DMA unmap from drivers')
refactored some code which resulted in an unused function in the at_hdmac
driver:

drivers/dma/at_hdmac_regs.h:350:23: warning: 'chan2parent' defined but
    not used [-Wunused-function]

Fixes: 54f8d501e8 ('dmaengine: remove DMA unmap from drivers')
Signed-off-by: Olof Johansson <olof@lixom.net>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Acked-by: Vinod Koul <vinod.koul@Intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/dma/at_hdmac_regs.h

@@ -347,10 +347,6 @@ static struct device *chan2dev(struct dma_chan *chan)
 {
 	return &chan->dev->device;
 }
-static struct device *chan2parent(struct dma_chan *chan)
-{
-	return chan->dev->device.parent;
-}
 
 #if defined(VERBOSE_DEBUG)
 static void vdbg_dump_regs(struct at_dma_chan *atchan)