xed_mbuild: fix install_dir initialization. using None
xed_mbuild: fix install_dir initialization. using None

Change-Id: I529c4fd0fc1dc9d31ee3b750f94df212d34861f2
(cherry picked from commit ac7e18baca74e95bfe35ecc209195417268974dd)

intelxed/xed,intelxed/xed,intelxed/xed,intelxed/xed