ASoC: Include linux/io.h for jz4740 codec

Include linux/io.h to fix below build errors:

  CC      sound/soc/codecs/jz4740.o
sound/soc/codecs/jz4740.c: In function 'jz4740_codec_read':
sound/soc/codecs/jz4740.c:82: error: implicit declaration of function 'readl'
sound/soc/codecs/jz4740.c: In function 'jz4740_codec_write':
sound/soc/codecs/jz4740.c:92: error: implicit declaration of function 'writel'
sound/soc/codecs/jz4740.c: In function 'jz4740_codec_probe':
sound/soc/codecs/jz4740.c:373: error: implicit declaration of function 'ioremap'
sound/soc/codecs/jz4740.c:373: warning: assignment makes pointer from integer without a cast
sound/soc/codecs/jz4740.c:393: error: implicit declaration of function 'iounmap'
make[3]: *** [sound/soc/codecs/jz4740.o] Error 1
make[2]: *** [sound/soc/codecs] Error 2
make[1]: *** [sound/soc] Error 2
make: *** [sound] Error 2

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>