sunrast: Remove if (unsigned int < 0) check.

Note: This fixes the following GCC warning :-
libavcodec/sunrast.c:94: warning: comparison of unsigned expression < 0 is always false.
Signed-off-by: Ronald S. Bultje <rsbultje@gmail.com>

libavcodec/sunrast.c

@@ -93,7 +93,7 @@ static int sunrast_decode_frame(AVCodecContext *avctx, void *data,
         av_log(avctx, AV_LOG_ERROR, "unsupported (compression) type\n");
         return -1;
     }
-    if (type < RT_OLD || type > RT_FORMAT_IFF) {
+    if (type > RT_FORMAT_IFF) {
         av_log(avctx, AV_LOG_ERROR, "invalid (compression) type\n");
         return -1;
     }