kbuild: Fix out-of-tree build for 'make deb-pkg'

The out-of-tree build is broken in 'make deb-pkg'. The
header checks and the header install works on the source and
not on the object tree.
While fixing this also replace the direct 'make' invocations
with the $MAKE variable to be consistent within the script.

Cc: maximilian attems <max@stro.at>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: debian-kernel@lists.debian.org
Cc: linux-kbuild@vger.kernel.org
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>