Update lang and ffmpeg submodules.

Updates ffmpeg to https://github.com/hrydgard/ppsspp-ffmpeg/commit/926573efd237bb47770c2117cdc3de472559eb7f.

Updates lang to https://github.com/hrydgard/ppsspp-lang/commit/e5990f704a05a55d8717135fca23afc345fc469a.