Prototype device structure to ensure LinuxKPI header file can be

included standalone.

MFC after:		1 week
Sponsored by:		Mellanox Technologies

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

@@ -49,6 +49,8 @@
 enum irqreturn	{ IRQ_NONE = 0, IRQ_HANDLED, IRQ_WAKE_THREAD, };
 typedef enum irqreturn	irqreturn_t;
 
+struct device;
+
 struct class {
 	const char	*name;
 	struct module	*owner;