ALSA: usb-audio: include format.h in format.c

Just in case a prototype changes, we'll be warned. This also fixes a
sparse warning.
Signed-off-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/format.c

@@ -30,6 +30,7 @@
 #include "helper.h"
 #include "debug.h"
 #include "clock.h"
+#include "format.h"
 
 /*
  * parse the audio format type I descriptor