arm: mvebu: a38x: Add const to some function calls

Functions that do not modify the pointer passed should declare it
as const.

Signed-off-by: Kevin Smith <kevin.smith@elecsyscorp.com>
Acked-by: Stefan Roese <sr@denx.de>
Cc: Dirk Eibach <eibach@gdsys.de>
Cc: Luka Perkov <luka.perkov@sartura.hr>