staging: usbip: changed function return type to void

commit ac2b41acfa3efe4650102067a99251587a806d70 upstream.

The function usbip_pad_iso never returns anything but 0 (success).

Signed-off-by: Bart Westgeest <bart@elbrys.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>