ALSA: line6: Add high-speed USB support

This has two parts:
* intervals_per_second setup
  (high speed needs 8000, instead of 1000)
* iso_buffers setup (count of iso buffers depends on
  USB speed, 2 is not enough for high speed)

Signed-off-by: Andrej Krutak <dev@andree.sk>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/line6/pcm.h

@@ -20,9 +20,6 @@
 
 #include "driver.h"
 
-/* number of URBs */
-#define LINE6_ISO_BUFFERS	2
-
 /*
 	number of USB frames per URB
 	The Line 6 Windows driver always transmits two frames per packet, but
@@ -31,7 +28,9 @@
 */
 #define LINE6_ISO_PACKETS	1
 
-/* in a "full speed" device (such as the PODxt Pro) this means 1ms */
+/* in a "full speed" device (such as the PODxt Pro) this means 1ms,
+ *  for "high speed" it's 1/8ms
+ */
 #define LINE6_ISO_INTERVAL	1
 
 #define LINE6_IMPULSE_DEFAULT_PERIOD 100