Change the subprocess argument to fix the build issue

Change subprocess arguments in  kernel_headers.py
script so that it can include dirname to resolve the
compilation issues in the new build system.

Change-Id: I89bbe53aa8a8b50e2c98a795fa20a976f2792a3b
Signed-off-by: Bharat Pawar <bpawar@codeaurora.org>
Signed-off-by: Srinivasarao P <spathi@codeaurora.org>