drm/i915/cnp+: update to the new RAWCLK_FREQ recommendations

drm/i915/cnp+: update to the new RAWCLK_FREQ recommendations

BSpec was updated and now there's no more "subtract 1" to the
Microsecond Counter Divider field.

It seems this should help fixing some GMBUS issues. I'm not aware of
any specific open bug that could be solved by this patch.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181112232313.26373-1-paulo.r.zanoni@intel.com