Fix out-of-tree builds with --enable-hardcoded-tables

Originally committed as revision 20404 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/costablegen.c

@@ -37,7 +37,7 @@ int main(int argc, char *argv[])
     double (*func)(double) = do_sin ? sin : cos;
 
     printf("/* This file was generated by libavcodec/costablegen */\n");
-    printf("#include \"dsputil.h\"\n");
+    printf("#include \"libavcodec/dsputil.h\"\n");
     for (i = 4; i <= BITS; i++) {
         int m = 1 << i;
         double freq = 2*M_PI/m;