There's no need to try to be cute with the include file locations in the
Makefile, so just specify exactly where the files are.

Bonus is this fixes the problem of building with O= as well as trying to
just build the subdirectory alone.
Reported-by: NStephen Rothwell <sfr@canb.auug.org.au>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Omer Shpigelman <oshpigelman@habana.ai>
Cc: Tomer Tayar <ttayar@habana.ai>
Cc: Moti Haimovski <mhaimovski@habana.ai>
Cc: Ofir Bitton <obitton@habana.ai>
Cc: Ben Segal <bpsegal20@gmail.com>
Cc: Christine Gharzuzi <cgharzuzi@habana.ai>
Cc: Pawel Piskorski <ppiskorski@habana.ai>
Link: https://lore.kernel.org/r/20200728171851.55842-1-gregkh@linuxfoundation.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>