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

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

Convert the inline functions MSeries_PLL_Divisor_Bits() and
MSeries_PLL_Multiplier_Bits() to macros. The helper function
ni_mseries_get_pll_parameters() always returns valid values for the
'divisor' and 'multiplier' so the sanity checking can safely be
removed.

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>