anim_util: quiet implicit conv warnings in 32-bit

the sizes are already validated by CheckSizeForOverflow(), add casts to
size_t to avoid -Wshorten-64-to-32

Change-Id: Ida9102c2104f4a334a0ad16d6e01a12bedfd4eec
(cherry picked from commit 1e2e25b0d4349e2bd6ef95d791fbf651b5e52cc0)
1 file changed