[ALSA] usb-audio - fix synchronization packet interval with Audigy 2 NX

USB generic driver
When a device does not provide the bRefresh field in its audio endpoint
descriptors, use the bInterval field instead.

Furthermore, increase the number of sync URBs for better queueing.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
1 file changed