Add RTC VIM1 Android 7 Nougat

Hi, I want to ask about Add RTC in Android 7
i was enable the deconfig and i added the dts code :
&i2c_b {
status = “okay”;
rtc_b: rtc_ds1307@68 {
compatible = “ds1307”;
reg = <0x68>;

show error hardware clock :
[ 2.133656@0] rtc-ds1307 2-0068: rtc core: registered ds1307 as rtc0
[ 2.138928@0] rtc-ds1307 2-0068: 56 bytes nvram
[ 5.002838@0] rtc-ds1307 2-0068: hctosys: unable to read the hardware clock

when i using hwclock command :

hwclock -w

hwclock: /dev/misc/rtc: No such file or directory

Anyone can help me to solve this issue?

the VIM1 already has an onboard RTC, just plug in the battery.