staging: comedi: ni_mio_common: remove unused variable in ni_ao_fifo_load()

The local variable 'range' is set but never used. Remove it.

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>