batman-adv: Annotate functions with format strings

Signed-off-by: Sven Eckelmann <sven@narfation.org>
diff --git a/net/batman-adv/bat_debugfs.c b/net/batman-adv/bat_debugfs.c
index abaeec5..4577d3f 100644
--- a/net/batman-adv/bat_debugfs.c
+++ b/net/batman-adv/bat_debugfs.c
@@ -50,6 +50,7 @@
 		debug_log->log_start = debug_log->log_end - log_buff_len;
 }
 
+__printf(2, 3)
 static int fdebug_log(struct debug_log *debug_log, char *fmt, ...)
 {
 	va_list args;