dmaengine: imx-dma.c: Remove unused function

Remove the function is_imx21_dma() that is not used anywhere.

This was partially found by using a static code analysis program called cppcheck.
Signed-off-by: Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/imx-dma.c

@@ -230,11 +230,6 @@ static inline int is_imx1_dma(struct imxdma_engine *imxdma)
 	return imxdma->devtype == IMX1_DMA;
 }
 
-static inline int is_imx21_dma(struct imxdma_engine *imxdma)
-{
-	return imxdma->devtype == IMX21_DMA;
-}
-
 static inline int is_imx27_dma(struct imxdma_engine *imxdma)
 {
 	return imxdma->devtype == IMX27_DMA;