staging: comedi: ni_mio_common: remove BUG_ON(gpct_index ...) checks

The gpct_index will always be 0 or 1. Remove the unnecessary BUG_ON()
checks.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>