iommu/unisoc: Fix spelling mistake "sixe" -> "size"

There is a spelling mistake in a dev_err message. Fix it.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20210319095750.5624-1-colin.king@canonical.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>