staging: sm7xxfb: rename vars holding device and revision ids

This patch fixes CamelCase var names in smtcfb_info holding device and
revision identifiers.

Tested with SM712.

Signed-off-by: Javier M. Mellid <jmunhoz@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>