files: don't compare unsigned value against 0

CID 1042292 (#1 of 1): Unsigned compared against 0 (NO_EFFECT)
unsigned_compare: This less-than-zero comparison of an unsigned value is
never true. "len < 0UL"
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

files.c

@@ -138,7 +138,7 @@ int do_dump_gen_file(struct fd_parms *p, int lfd,
 
 int fill_fdlink(int lfd, const struct fd_parms *p, struct fd_link *link)
 {
-	size_t len;
+	int len;
 
 	link->name[0] = '.';