avformat/http: Fix 2 typos

Found-by: wm4
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/http.c

@@ -946,7 +946,7 @@ static int http_buf_read(URLContext *h, uint8_t *buf, int size)
         if (!len && (!s->willclose || s->chunksize < 0) &&
             s->filesize >= 0 && s->off < s->filesize) {
             av_log(h, AV_LOG_ERROR,
-                   "Streams ends prematurly at %"PRId64", should be %"PRId64"\n",
+                   "Stream ends prematurely at %"PRId64", should be %"PRId64"\n",
                    s->off, s->filesize
                   );
             return AVERROR(EIO);