Fix linking to libav in non-default path

LIBAV_LDFLAGS has -L, LIBAV_LIBRARIES is just the names of the

I think this is not necessary for other dependencies because they
consist of a single library and go through a different path (check_lib)
that provides the full path to it. e.g. from my CMakeCache.txt:

ICONV_LIBRARIES:FILEPATH=/usr/lib/libiconv.dylib (good)
LIBAV_LIBRARIES:INTERNAL=avcodec;avformat;swscale;avutil (bad)

0 files changed, 0 insertions, 0 deletions