dmaengine: pch_dma: remove unused function chan2parent

The helper function chan2parent is not used and has never been
used since the first commit to the code back in 2010. The function
is redundant and can be removed.

Cleans up clang scan build warning:
drivers/dma/pch_dma.c:158:30: warning: unused function 'chan2parent' [-Wunused-function]

Signed-off-by: Colin Ian King <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

drivers/dma/pch_dma.c

···
 	return &chan->dev->device;
 }
 
-static inline struct device *chan2parent(struct dma_chan *chan)
-{
-	return chan->dev->device.parent;
-}
-
 static inline
 struct pch_dma_desc *pdc_first_active(struct pch_dma_chan *pd_chan)
 {