iommu/arm-smmu-v3: Fix resource_size check

This is an off-by-one mistake.

resource_size() returns res->end - res->start + 1.

Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Will Deacon <will@kernel.org>