staging: comedi: ni_tio: tidy up enum ni_m_series_clock_source

These values are not used as an enum. For aesthetics, rename the
CamelCase values and convert them into defines.

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>

diff --cc drivers/staging/comedi/drivers/ni_tio.c
Simple merge