zram: simplify and optimize dev_to_zram()

Simplify and optimize dev_to_zram() without walking the zram_devices
array.

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/zram/zram_sysfs.c

@@ -30,18 +30,9 @@ static u64 zram_stat64_read(struct zram *zram, u64 *v)
 	return val;
 }
 
-static struct zram *dev_to_zram(struct device *dev)
+static inline struct zram *dev_to_zram(struct device *dev)
 {
-	int i;
-	struct zram *zram = NULL;
-
-	for (i = 0; i < zram_get_num_devices(); i++) {
-		zram = &zram_devices[i];
-		if (disk_to_dev(zram->disk) == dev)
-			break;
-	}
-
-	return zram;
+	return (struct zram *)dev_to_disk(dev)->private_data;
 }
 
 static ssize_t disksize_show(struct device *dev,