We need to pass the location sdl-config so that ffmpeg picks it up.
So just pass the whole string to make things simpler.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>

diff -Nura ffmpeg-0.8.7.orig/configure ffmpeg-0.8.7/configure
--- ffmpeg-0.8.7.orig/configure	2011-11-21 16:49:30.000000000 -0300
+++ ffmpeg-0.8.7/configure	2011-12-02 08:13:36.746619395 -0300
@@ -2957,7 +2957,7 @@
 enabled libxvid    && require  libxvid xvid.h xvid_global -lxvidcore
 enabled mlib       && require  mediaLib mlib_types.h mlib_VectorSub_S16_U8_Mod -lmlib
 
-SDL_CONFIG="${cross_prefix}sdl-config"
+SDL_CONFIG="${SDL_CONFIG}"
 if check_pkg_config sdl SDL_version.h SDL_Linked_Version; then
     check_cpp_condition SDL.h "(SDL_MAJOR_VERSION<<16 | SDL_MINOR_VERSION<<8 | SDL_PATCHLEVEL) >= 0x010201" $sdl_cflags &&
     enable sdl &&