Staging: zram: Fix variable dereferenced before check

This patch fixes the following Smatch warning in zram_drv.c-
drivers/staging/zram/zram_drv.c:899
destroy_device() warn: variable dereferenced before check 'zram->disk' (see line 896)
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Rashika Kheria <rashika.kheria@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/zram/zram_drv.c

@@ -896,12 +896,9 @@ static void destroy_device(struct zram *zram)
 	sysfs_remove_group(&disk_to_dev(zram->disk)->kobj,
 			&zram_disk_attr_group);
 
-	if (zram->disk) {
 	del_gendisk(zram->disk);
 	put_disk(zram->disk);
-	}
 
-	if (zram->queue)
 	blk_cleanup_queue(zram->queue);
 }