vf_detc: dont mix av_strdup & free

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/libmpcodecs/vf_detc.c

@@ -412,7 +412,7 @@ static void parse_var(struct vf_priv_s *p, char *var)
 static void parse_args(struct vf_priv_s *p, char *args)
 {
         char *next, *orig;
-        for (args=orig=av_strdup(args); args; args=next) {
+        for (args=orig=strdup(args); args; args=next) {
                 next = strchr(args, ':');
                 if (next) *next++ = 0;
                 parse_var(p, args);