staging: comedi: fix up missing whitespace in comment

I noticed this missing whitespace in a comment inside ni_mio_common.c

Signed-off-by: Garrit Franke <garritfranke@gmail.com>
Link: https://lore.kernel.org/r/20200615135541.46986-1-garritfranke@gmail.com


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