device: constify some variables

Change-Id: I6830a65bc9cea2907f4209bb97a53ccebcbf248d
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Reviewed-on: https://review.coreboot.org/25873
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
4 files changed