err macro has been removed entirely from the Linux kernel starting from
around v3.5, while the dbg macro has been deprecated. Since the lines
that were using err/dbg did not have access to the device, simply log as
a generic kernel log.
Due to plans to scrap the kernel module approach and go with a full-fledged
userspace application, this commit renames the driver folder to kernel_module
so the folder contents are clear.