Increase the bulk-out buffer size from 64 to 256 byte.

This gives a significant increase in throughput already at 1Mbaud
(e.g. 710 instead of 640 KB/s) as well as lowered CPU usage.
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>