ALSA: line6: Enable different number of URBs for frame transfers

This basically changes LINE6_ISO_BUFFERS constant to a configurable
iso_buffers property.

Signed-off-by: Andrej Krutak <dev@andree.sk>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/usb/line6/driver.h b/sound/usb/line6/driver.h
index 7da643e..43dd1d0 100644
--- a/sound/usb/line6/driver.h
+++ b/sound/usb/line6/driver.h
@@ -111,6 +111,8 @@
 
 	/* Interval (ms) */
 	int interval;
+	/* Number of isochronous URBs used for frame transfers */
+	int iso_buffers;
 
 	/* Maximum size of USB packet */
 	int max_packet_size;