linuxkpi: Add dev_warn_once() in <linux/device.h>

Reviewed by:	manu
Approved by:	manu
Differential Revision:	https://reviews.freebsd.org/D36968

sys/compat/linuxkpi/common/include/linux/device.h

@@ -206,6 +206,14 @@ show_class_attr_string(struct class *class,
 	}					\
 } while (0)
 
+#define	dev_warn_once(dev, ...) do {		\
+	static bool __dev_warn_once;		\
+	if (!__dev_warn_once) {			\
+		__dev_warn_once = 1;		\
+		dev_warn(dev, __VA_ARGS__);	\
+	}					\
+} while (0)
+
 #define	dev_err_once(dev, ...) do {		\
 	static bool __dev_err_once;		\
 	if (!__dev_err_once) {			\