UAPI: Guard linux/sound.h

Place reinclusion guards on linux/sound.h otherwise the UAPI splitter script
won't insert a #include to make the kernel header include the UAPI header.
Signed-off-by: David Howells <dhowells@redhat.com>

include/linux/sound.h

+#ifndef _LINUX_SOUND_H
+#define _LINUX_SOUND_H
 
 /*
  * Minor numbers for the sound driver.
@@ -42,3 +44,5 @@ extern void unregister_sound_mixer(int unit);
 extern void unregister_sound_midi(int unit);
 extern void unregister_sound_dsp(int unit);
 #endif /* __KERNEL__ */
+
+#endif /* _LINUX_SOUND_H */