avcodec/rawdec: Fix bits_per_coded_sample checks

Fixes assertion failure
Fixes: 9eb9cf5b8c26dd0fa7107ed0348dcc1f/signal_sigabrt_7ffff6ae7c37_8926_4609a5c3f071d555d2d557625f9687b1.swf

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
