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-0.6.1/configure ffmpeg-0.6.1.sdl/configure
--- ffmpeg-0.6.1/configure	2010-06-15 16:44:30.000000000 -0300
+++ ffmpeg-0.6.1.sdl/configure	2011-02-25 17:13:12.979168176 -0300
@@ -2640,7 +2640,7 @@
     die "ERROR: No version of libdc1394 found "
 fi
 
-SDL_CONFIG="${cross_prefix}sdl-config"
+SDL_CONFIG="${SDL_CONFIG}"
 if "${SDL_CONFIG}" --version > /dev/null 2>&1; then
     sdl_cflags=$("${SDL_CONFIG}" --cflags)
     sdl_libs=$("${SDL_CONFIG}" --libs)