jpeg2000dec: Use correct printf length modifier for pointer differences

Also eliminate an unnecessary cast. Fixes the following warning:
jpeg2000dec.c:1200:20: warning: format ‘%lX’ expects argument of type ‘long unsigned int’, but argument 5 has type ‘long long unsigned int’

libavcodec/jpeg2000dec.c

@@ -1196,8 +1196,8 @@ static int jpeg2000_read_main_headers(Jpeg2000DecoderContext *s)
             break;
         default:
             av_log(s->avctx, AV_LOG_ERROR,
-                   "unsupported marker 0x%.4X at pos 0x%lX\n",
-                   marker, (uint64_t)(s->buf - s->buf_start - 4));
+                   "unsupported marker 0x%.4X at pos 0x%tX\n",
+                   marker, s->buf - s->buf_start - 4);
             s->buf += len - 2;
             break;
         }