refactor: use C23 attribute syntax

Change-Id: I42a150e0895fe6f8be397ff33f7ff0d8ca63df47
Signed-off-by: Karl Meakin <karl.meakin@arm.com>
diff --git a/inc/hf/dlog.h b/inc/hf/dlog.h
index 954f8eb..270306d 100644
--- a/inc/hf/dlog.h
+++ b/inc/hf/dlog.h
@@ -57,7 +57,7 @@
 };
 
 void dlog_enable_lock(void);
-__attribute__((format(printf, 1, 2))) size_t dlog(const char *fmt, ...);
+[[gnu::format(printf, 1, 2)]] size_t dlog(const char *fmt, ...);
 size_t vdlog(const char *fmt, struct va_list_wrapper *args);
 
 /*