wmalosslessdec: fix mclms_coeffs* array size

Fixes corruption of context

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC:libav-stable@libav.org
Bug-Id: CVE-2014-2098
Signed-off-by: Anton Khirnov <anton@khirnov.net>
