Building external (out of tree) module into kernel of Buildroot

I saw DS1621 is a temperature sensor, and the driver is already in drivers/hwmon/ds1621.c in a standard open source Linux kernel tree, this means to make use of it all you need to do is to turn it on, and re-compile the kernel.

I've no idea why you implement the driver yourself and construct the Makefile in your own way--now with error, but I would suggest you to move back to the conventional way, just to make use of the existing driver.

I saw DS1621 is a temperature sensor, and the driver is already in drivers/hwmon/ds1621.c in a standard open source Linux kernel tree, this means to make use of it all you need to do is to turn it on, and re-compile the kernel.

I've no idea why you implement the driver yourself and construct the Makefile in your own way--now with error, but I would suggest you to move back to the conventional way, just to make use of the existing driver.