lib/fs/readlink/readlinknul.h: readlinknul(): Simplify the return value

We don't use the length at call site.  Just return 0 for success.

Signed-off-by: Alejandro Colomar <alx@kernel.org>

lib/fs/readlink/readlinknul.h

@@ -43,7 +43,7 @@ readlinknul(const char *restrict link, char *restrict buf, size_t size)
 	}
 
 	stpcpy(&buf[len], "");
-	return len;
+	return 0;
 }