Globally replace $(HOST_DIR)/usr/sbin with $(HOST_DIR)/sbin

Since things are no longer installed in $(HOST_DIR)/usr, the callers
should also not refer to it.

This is a mechanical change with
git grep -l '$(HOST_DIR)/usr/sbin' | xargs sed -i 's%$(HOST_DIR)/usr/sbin%$(HOST_DIR)/sbin%g'

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>