Remove volatile qualifier in get_ram_size() calls

Remove volatile qualifier in get_ram_size() calls

Checkpatch.pl complains about the volatile qualifier in calls to
get_ram_size(). Remove this qualifier in the prototype and in the
calls where it is useless, and leave it only in the function body
where it is needed.

Signed-off-by: Albert ARIBAUD <albert.u.boot@aribaud.net>