img2: Drop av_ prefix for a static function

This prefix is reserved for public functions only.
Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>

libavformat/img2.c

@@ -82,7 +82,7 @@ static const IdStrMap img_tags[] = {
     { AV_CODEC_ID_NONE,       NULL       }
 };
 
-static enum AVCodecID av_str2id(const IdStrMap *tags, const char *str)
+static enum AVCodecID str2id(const IdStrMap *tags, const char *str)
 {
     str = strrchr(str, '.');
     if (!str)
@@ -100,5 +100,5 @@ static enum AVCodecID av_str2id(const IdStrMap *tags, const char *str)
 
 enum AVCodecID ff_guess_image2_codec(const char *filename)
 {
-    return av_str2id(img_tags, filename);
+    return str2id(img_tags, filename);
 }