Fixes many -Wenum-conversion warnings with Clang caused by
e6c2c870.
See e.g.
https://fate.ffmpeg.org/log.cgi?time=20240325033545&slot=aarch64-linux-clang-10&log=compileReviewed-by: Henrik Gramner <henrik@gramner.com>
Reviewed-by: James Almer <jamrial@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>