ALSA: usb-audio: Expose sample resolution through proc interface

At least some USB devices use (MSB-aligned) audio format larger
than the actual resolution of the device. In order to expose the
actual device resolution (bBitResolution), add extra field to the
procfs stream info interface.

Signed-off-by: Jussi Laako <jussi@sonarnerd.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/card.h

@@ -14,6 +14,7 @@ struct audioformat {
 	u64 formats;			/* ALSA format bits */
 	unsigned int channels;		/* # channels */
 	unsigned int fmt_type;		/* USB audio format type (1-3) */
+	unsigned int fmt_bits;		/* number of significant bits */
 	unsigned int frame_size;	/* samples per frame for non-audio */
 	int iface;			/* interface number */
 	unsigned char altsetting;	/* corresponding alternate setting */