avformat/mov: Fix mixed declaration and statement warning

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

libavformat/mov.c

@@ -214,10 +214,11 @@ static int mov_read_covr(MOVContext *c, AVIOContext *pb, int type, int len)
 static int mov_metadata_raw(MOVContext *c, AVIOContext *pb,
                             unsigned len, const char *key)
 {
+    char *value;
     // Check for overflow.
     if (len >= INT_MAX)
         return AVERROR(EINVAL);
-    char *value = av_malloc(len + 1);
+    value = av_malloc(len + 1);
     if (!value)
         return AVERROR(ENOMEM);
     avio_read(pb, value, len);