[media] media-device.h: fix compiler warning

Fix these compiler warnings:

media-git/include/media/media-device.h: In function 'media_device_pci_init':
media-git/include/media/media-device.h:610:9: warning: 'return' with a value, in function returning void
  return NULL;
         ^
media-git/include/media/media-device.h: In function '__media_device_usb_init':
media-git/include/media/media-device.h:618:9: warning: 'return' with a value, in function returning void
  return NULL;
         ^
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

include/media/media-device.h

@@ -693,7 +693,6 @@ static inline void media_device_pci_init(struct media_device *mdev,
 					 struct pci_dev *pci_dev,
 					 char *name)
 {
-	return NULL;
 }
 
 static inline void __media_device_usb_init(struct media_device *mdev,
@@ -701,7 +700,6 @@ static inline void __media_device_usb_init(struct media_device *mdev,
 					   char *board_name,
 					   char *driver_name)
 {
-	return NULL;
 }
 
 #endif /* CONFIG_MEDIA_CONTROLLER */