xen/xenbus: fix W=1 build warning in xenbus_va_dev_error function

This patch fixes a W=1 format-string warning reported by GCC 12.3.0
by annotating xenbus_switch_fatal() and xenbus_va_dev_error()
with the __printf attribute. The attribute enables compile-time
validation of printf-style format strings in these functions.

The original warning trace:
drivers/xen/xenbus/xenbus_client.c:304:9: warning: function 'xenbus_va_dev_error' might be
a candidate for 'gnu_printf' format attribute [-Wsuggest-attribute=format]

Signed-off-by: Peng Jiang <[email protected]>
Reviewed-by: Juergen Gross <[email protected]>
Message-ID: <[email protected]>
Signed-off-by: Juergen Gross <[email protected]>

Author: Jump2233

drivers/xen/xenbus/xenbus_client.c

@@ -202,6 +202,7 @@ int xenbus_watch_pathfmt(struct xenbus_device *dev,
 }
 EXPORT_SYMBOL_GPL(xenbus_watch_pathfmt);
 
+__printf(4, 5)
 static void xenbus_switch_fatal(struct xenbus_device *, int, int,
 				const char *, ...);
 
@@ -287,6 +288,7 @@ int xenbus_frontend_closed(struct xenbus_device *dev)
 }
 EXPORT_SYMBOL_GPL(xenbus_frontend_closed);
 
+__printf(3, 0)
 static void xenbus_va_dev_error(struct xenbus_device *dev, int err,
 				const char *fmt, va_list ap)
 {