ASoC: fix compile breakage of the sh/siu driver

The sh/siu ASoC driver doesn't compile because of a function defined static in
the source and extern in a header. Remove the unneeded declaration in the
header.
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/sh/siu.h

@@ -182,7 +182,6 @@ static inline u32 siu_read32(u32 __iomem *addr)
 #define SIU_BRRB	(0x10c / sizeof(u32))
 
 extern struct snd_soc_platform_driver siu_platform;
-extern struct snd_soc_dai_driver siu_i2s_dai;
 extern struct siu_info *siu_i2s_data;
 
 int siu_init_port(int port, struct siu_port **port_info, struct snd_card *card);