target: fix deprecated attribute names in dmesg

The following message is displayed in dmesg when a deprecated attribute
is set:

  "ignoring deprecated ##_name## attribute"

This patch fixes the format to include the name of the deprecated
attribute.

Signed-off-by: Christophe Vu-Brugier <cvubrugier@fastmail.fm>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_configfs.c

@@ -549,7 +549,8 @@ static ssize_t _name##_store(struct config_item *item, const char *page,\
 		size_t count)						\
 {									\
 	printk_once(KERN_WARNING					\
-		"ignoring deprecated ##_name## attribute\n");	\
+		"ignoring deprecated %s attribute\n",			\
+		__stringify(_name));					\
 	return count;							\
 }