id3v2: prefer TDRC for date over TDRL.

TDRL is what we used as a replacement of TYER, and, according to
http://id3.org/id3v2.4.0-changes :
    TYER - Year
        This frame is replaced by the TDRC frame, 'Recording time'
        [F:4.2.5].
So change TDRL usages to TDRC.

Fixes ticket #3694
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/id3v2.c

@@ -60,8 +60,8 @@ const AVMetadataConv ff_id3v2_34_metadata_conv[] = {
 
 const AVMetadataConv ff_id3v2_4_metadata_conv[] = {
     { "TCMP", "compilation"   },
-    { "TDRL", "date"          },
     { "TDRC", "date"          },
+    { "TDRL", "date"          },
     { "TDEN", "creation_time" },
     { "TSOA", "album-sort"    },
     { "TSOP", "artist-sort"   },

libavformat/mp3enc.c

@@ -58,7 +58,7 @@ static int id3v1_create_tag(AVFormatContext *s, uint8_t *buf)
     count += id3v1_set_string(s, "TIT2",    buf +  3, 30 + 1);       //title
     count += id3v1_set_string(s, "TPE1",    buf + 33, 30 + 1);       //author|artist
     count += id3v1_set_string(s, "TALB",    buf + 63, 30 + 1);       //album
-    count += id3v1_set_string(s, "TDRL",    buf + 93,  4 + 1);       //date
+    count += id3v1_set_string(s, "TDRC",    buf + 93,  4 + 1);       //date
     count += id3v1_set_string(s, "comment", buf + 97, 30 + 1);
     if ((tag = av_dict_get(s->metadata, "TRCK", NULL, 0))) { //track
         buf[125] = 0;