staging: comedi: remove unused variable 'route_table_size'

drivers/staging/comedi/drivers/ni_routes.c:52:21: warning:
 route_table_size defined but not used [-Wunused-const-variable=]

It is never used since introduction.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20191023075206.33088-1-yuehaibing@huawei.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>