drm_hwcomposer: Add safe guard for unknown connector type

There is potential possibility that new connector type will be added
into DRM and it won't be handled by drm_hwcomposer immediately so it's
better to be safe and report error via logcat than crash with
out-of-bounds.

Signed-off-by: Roman Kovalivskyi <roman.kovalivskyi@globallogic.com>