Fix linking: emms_c is a macro, #include the correct header file.

Originally committed as revision 9238 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/grab.c

@@ -19,6 +19,7 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 #include "avformat.h"
+#include "dsputil.h"
 #include <unistd.h>
 #include <fcntl.h>
 #include <sys/ioctl.h>