[ALSA] Add SUPERH depends to sound/soc/sh/Kconfig

Currently you will see an empty "SoC Audio support for SuperH" menu
when building for other archs (example pxa).
This patch adds "depends on SUPERH" to remove that empty menu.
Signed-off-by: Kristoffer Ericson <kristoffer.ericson@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/soc/sh/Kconfig

 menu "SoC Audio support for SuperH"
+	depends on SUPERH
 
 config SND_SOC_PCM_SH7760
 	tristate "SoC Audio support for Renesas SH7760"