rtc: ds1307: use sysfs_emit() to instead of scnprintf()

Follow the advice of the Documentation/filesystems/sysfs.rst and show()
should only use sysfs_emit() or sysfs_emit_at() when formatting the
value to be returned to user space.

Signed-off-by: ye xingchen <ye.xingchen@zte.com.cn>
Link: https://lore.kernel.org/r/202212051134455911470@zte.com.cn
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-ds1307.c

@@ -1219,8 +1219,7 @@ static ssize_t frequency_test_show(struct device *dev,
 
 	regmap_read(ds1307->regmap, M41TXX_REG_CONTROL, &ctrl_reg);
 
-	return scnprintf(buf, PAGE_SIZE, (ctrl_reg & M41TXX_BIT_FT) ? "on\n" :
-			"off\n");
+	return sysfs_emit(buf, (ctrl_reg & M41TXX_BIT_FT) ? "on\n" : "off\n");
 }
 
 static DEVICE_ATTR_RW(frequency_test);