rtc: ds1305: use to_spi_device and kobj_to_dev

For better readability, use to_spi_device() and kobj_to_dev() instead
of container_of().
Signed-off-by: Geliang Tang <geliangtang@163.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

drivers/rtc/rtc-ds1305.c

@@ -532,7 +532,7 @@ ds1305_nvram_read(struct file *filp, struct kobject *kobj,
 	struct spi_transfer	x[2];
 	int			status;
 
-	spi = container_of(kobj, struct spi_device, dev.kobj);
+	spi = to_spi_device(kobj_to_dev(kobj));
 
 	addr = DS1305_NVRAM + off;
 	msg_init(&m, x, &addr, count, NULL, buf);
@@ -554,7 +554,7 @@ ds1305_nvram_write(struct file *filp, struct kobject *kobj,
 	struct spi_transfer	x[2];
 	int			status;
 
-	spi = container_of(kobj, struct spi_device, dev.kobj);
+	spi = to_spi_device(kobj_to_dev(kobj));
 
 	addr = (DS1305_WRITE | DS1305_NVRAM) + off;
 	msg_init(&m, x, &addr, count, buf, NULL);