avfilter/af_hdcd: Use int32_t instead of int for gaintable in hdcd filter.

Signed-off-by: Benjamin Steffes <benjaminst123@gmail.com>

(comment by ronald)
prevent the theoretical case where the container type (int)
would be 64 bit on some platforms, which would waste some space

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
