avutil/adler32: Switch av_adler32_update() to size_t on bump

avutil/adler32: Switch av_adler32_update() to size_t on bump

av_adler32_update() is used by av_hash_update() which will be switched
to size_t at the next bump. So it also has to be made to use size_t.
This is also necessary for framecrcenc.c, because the size of side data
will become a size_t, too.

Reviewed-by: James Almer <jamrial@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>