aspeed: remove useless comment on controller segment size

The flash devices used for the FMC controller (BMC firmware) are well
defined for each Aspeed machine and are all smaller than the default
mapping window size, at least for CE0 which is the chip the SoC boots
from.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 1486648058-520-3-git-send-email-clg@kaod.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>