staging: comedi: ni_stc.h: tidy up NI_M_CLK_FOUT2_REG bits

Rename the CamelCase and convert the enum into defines. Use the BIT()
macro to define the bits.

Convert the inline function MSeries_PLL_In_Source_Select_RTSI_Bits()
to a macro. The caller always passes valid values for 'RTIS_channel'
so the sanity checking can safely be removed.

Tidy up ni_mseries_set_pll_master_clock() to remove the unnecessary
extra indent level for the code that sets a RTSI channel for the
PLL source.

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>