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: NMinchan Kim <minchan@kernel.org>
Acked-by: NJerome Marchand <jmarchan@redhat.com>
Signed-off-by: NRashika Kheria <rashika.kheria@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/zram/zram_drv.c

@@ -896,13 +896,10 @@ 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);
-	}
+	del_gendisk(zram->disk);
+	put_disk(zram->disk);
 
-	if (zram->queue)
-		blk_cleanup_queue(zram->queue);
+	blk_cleanup_queue(zram->queue);
 }
 
 static int __init zram_init(void)