bootcounter_ram: Fix misaligned cache warning

This patch fixes the warning about misaligned cache on Armada XP:

CACHE: Misaligned operation at range [7ffff000, 7fffffac]

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Valentin Longchamp <valentin.longchamp@keymile.com>
Reviewed-by: Tom Rini <trini@konsulko.com>