twinvq: fix out of bounds array access

ModeTab.fmode has only 3 elements, so indexing it with ftype
in the initialier for 'size' is invalid when ftype == FT_PPC.

This fixes crashes with gcc 4.8.

Signed-off-by: Mans Rullgard <mans@mansr.com>
(cherry picked from commit 4bf2e7c5f1c0ad3997fd7c9859c16db8e4e16df6)
Signed-off-by: Diego Biurrun <diego@biurrun.de>