PM: core: Remove duplicate declaration from header file

struct device is declared twice, so remove the duplicate.
Signed-off-by: NWan Jiabing <wanjiabing@vivo.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

include/linux/pm.h

@@ -39,7 +39,6 @@ static inline void pm_vt_switch_unregister(struct device *dev)
  * Device power management
  */
 
-struct device;
 
 #ifdef CONFIG_PM
 extern const char power_group_name[];		/* = "power" */