kconfig: use va_end to match corresponding va_start

Although on some systems va_end is a no-op, it is good practice
to use va_end, especially since the manual states:

"Each invocation of va_start() must be matched by a corresponding
invocation of va_end() in the same function."
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Signed-off-by: NMichal Marek <mmarek@suse.cz>

scripts/kconfig/confdata.c

@@ -59,6 +59,7 @@ static void conf_message(const char *fmt, ...)
 	va_start(ap, fmt);
 	if (conf_message_callback)
 		conf_message_callback(fmt, ap);
+	va_end(ap);
 }
 
 const char *conf_get_configname(void)