drm/i915/vbt: Fix HDMI level shifter and max data rate bitfield sizes

The HDMI level shifter value should be 5 bits and the max data rate 3 bits.

Cc: Jani Nikula <jani.nikula@intel.com>
Reported-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171027201738.3640-1-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>