The input packets are always assumed to be padded and
the av_fast_ family of function takes a pointer to a pointer.

Thanks to Nicolas Dufresne <nicolas.dufresne@collabora.com> for
a similar patch.

Introduced in 7b588bb6.

Bug-Id: 766
CC: libav-stable@libav.org
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>