staging: comedi: ni_mio_common: remove 'fudge_factor_80_to_20Mhz'

For aesthetics, remove this local variable to fix the checkpatch.pl issue:
CHECK: Avoid CamelCase: <fudge_factor_80_to_20Mhz>

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>