Staging: comedi: Fixed camel case style issue in usbdux.c

This is a patch to usbdux.c that fixes the camel case warnings found
by the checkpatch.pl tool

Signed-off-by: Jacob Garber <ajtgarber@gmail.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>