init: Fix segfault when log_write() was missing an arg to format.

Also, flag log_write() as a printf-like beast to gcc.

Signed-off-by: Dima Zavin <dima@android.com>
diff --git a/init/init.h b/init/init.h
index b686869..c9363da 100644
--- a/init/init.h
+++ b/init/init.h
@@ -29,7 +29,8 @@
 void log_init(void);
 void log_set_level(int level);
 void log_close(void);
-void log_write(int level, const char *fmt, ...);
+void log_write(int level, const char *fmt, ...)
+    __attribute__ ((format(printf, 2, 3)));
 
 #define ERROR(x...)   log_write(3, "<3>init: " x)
 #define NOTICE(x...)  log_write(5, "<5>init: " x)