transport.c: help gcc 4.6.3 users by squelching compiler warning

To a human reader, it is quite obvious that cmp is assigned before
it is used, but gcc 4.6.3 that ships with Ubuntu 12.04 is among
those that do not get this right.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

transport.c

@@ -106,7 +106,8 @@ static void insert_packed_refs(const char *packed_refs, struct ref **list)
 		return;
 
 	for (;;) {
-		int cmp, len;
+		int cmp = 0; /* assigned before used */
+		int len;
 
 		if (!fgets(buffer, sizeof(buffer), f)) {
 			fclose(f);