ASoC: rsnd: Silence DMA slave ID compile warning on 64-bit

On arm64:

    sound/soc/sh/rcar/dma.c: In function 'rsnd_dmaen_init':
    sound/soc/sh/rcar/dma.c:180:9: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
	     (void *)id);
	     ^
    include/linux/dmaengine.h:1185:75: note: in definition of macro 'dma_request_channel'
     #define dma_request_channel(mask, x, y) __dma_request_channel(&(mask), x, y)
									       ^

Add an intermediate cast to "uintptr_t" to kill the compile warning.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Mark Brown <broonie@kernel.org>