Add in a workaround to allow the usb serial devices to work with the
usb pass through mechanism.  The ioctl() to request an alternate
interface will always return < 0 for a usb-serial device based on the
kernel driver.  This means there is no alternate interface end point.

This was fully tested with a pl2303 usb serial device.
Signed-off-by: NJason Wessel <jason.wessel@windriver.com>