avcodec/hevc_ps: Use get_bits_long() in decode_vui()

Fix assertion failure
Fixes: a225222ef88a0f5b1e93e1d0432debc3-asan_static-oob_124a17d_1448_cov_77608227_DBLK_E_VIXS_1.bit
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
