drm/i915/skl: Updated the gen6_init_rps_frequencies function

On SKL the frequency is specified in units of 16.66 MHZ, barring the
RP_STATE_CAP(0x5998) register, which still reports frequency in units
of 50 MHZ. So an extra conversion is required in gen6_init_rps_frequencies
function for SKL, to store the frequency values as per the actual hardware unit.

v2: Corrected the conversion from 50 to 16.66 MHZ (Ville)

Signed-off-by: Akash Goel <akash.goel@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>