net: wget: Fix comparison of unsigned variable

content_length is an unsigned long and so testing that it is >= 0 will
always be true. Instead test that it is != -1 as that is the condition
set on error.

This issue found by Smatch.

Signed-off-by: Andrew Goodbody <andrew.goodbody@linaro.org>
Reviewed-by: Jerome Forissier <jerome.forissier@linaro.org>

net/wget.c

@@ -214,7 +214,7 @@ static void tcp_stream_on_rcv_nxt_update(struct tcp_stream *tcp, u32 rx_bytes)
 			content_length = -1;
 	}
 
-	if (content_length >= 0) {
+	if (content_length != -1) {
 		debug_cond(DEBUG_WGET,
 			   "wget: Connected Len %lu\n",
 			   content_length);