cdrom: make unregister_cdrom() return void

Now unregister_cdrom() always returns 0.
Make it return void and update all callers that check the return value.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Adrian McMenamin <adrian@mcmen.demon.co.uk>
Cc: Borislav Petkov <petkovbb@gmail.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/include/linux/cdrom.h b/include/linux/cdrom.h
index 40e05d0..5db265e 100644
--- a/include/linux/cdrom.h
+++ b/include/linux/cdrom.h
@@ -995,7 +995,7 @@
 extern int cdrom_media_changed(struct cdrom_device_info *);
 
 extern int register_cdrom(struct cdrom_device_info *cdi);
-extern int unregister_cdrom(struct cdrom_device_info *cdi);
+extern void unregister_cdrom(struct cdrom_device_info *cdi);
 
 typedef struct {
     int data;