ASoC: kirkwood: fix compilation warning in kirkwood_dma_open

writel() supposes the first argument of type unsigned int. This fix the
warning:

sound/soc/kirkwood/kirkwood-dma.c: In function 'kirkwood_dma_open':
sound/soc/kirkwood/kirkwood-dma.c:164:3: warning: large integer implicitly
truncated to unsigned type [-Woverflow]
Signed-off-by: Vladimir Murzin <murzin.v@gmail.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

sound/soc/kirkwood/kirkwood-dma.c

@@ -159,7 +159,7 @@ static int kirkwood_dma_open(struct snd_pcm_substream *substream)
 		 * Enable Error interrupts. We're only ack'ing them but
 		 * it's useful for diagnostics
 		 */
-		writel((unsigned long)-1, priv->io + KIRKWOOD_ERR_MASK);
+		writel((unsigned int)-1, priv->io + KIRKWOOD_ERR_MASK);
 	}
 
 	dram = mv_mbus_dram_info();