Staging: comedi: drivers: ni_pcimio: Fix variable name

Fixed a variable name that was Camel case

Signed-off-by: Eric Yu <ejyu99@gmail.com>
Link: https://lore.kernel.org/r/20200503021247.250785-1-ejyu99@gmail.com


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