READ has already been undefined at this point; it is obviously intended
to undef WRITE.
Furthermore, leb128 (in cbs_av1) was undefined too often and
inconsistently.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Silences a warning with clang:
libavcodec/cbs_vp9_syntax_template.c:220:17: warning: implicit conversion from 'int' to 'int8_t' (aka 'signed char')
changes value from 255 to -1
