drm/i915/vbt: Child device size remains unchanged through VBT 229

drm/i915/vbt: Child device size remains unchanged through VBT 229

The latest documented version of the VBT is 229, but no further data has
been added to the child device definition in block 2.  Update the child
device version test to eliminate the "Expected child device config size
for VBT version XXX not known; assuming 39" debug messages from the
logs.

Bspec: 20124
Bspec: 20157
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191002192258.1013-1-matthew.d.roper@intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>