avoid failure if /lib/firmware doesn't exist

On Debian, /lib/firmware is provided by optional packages like
firmware-iwlwifi or firmware-linux-free. That's why this directory
may not exist.
This change ensure the directory exist before trying to copy it
content.

Change-Id: Icf9eedf4148141c92e9171f16ae744b88a8d8519
Merge "avoid failure if /lib/firmware doesn't exist"