ASoC: add missing inclusion of debugfs.h

To fix compile errors.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/soc/soc-dapm.c

@@ -37,6 +37,7 @@
 #include <linux/bitops.h>
 #include <linux/platform_device.h>
 #include <linux/jiffies.h>
+#include <linux/debugfs.h>
 #include <sound/core.h>
 #include <sound/pcm.h>
 #include <sound/pcm_params.h>