iommu/arm-smmu: Fix out-of-bounds dereference

When we iterate a master's config entries, what we generally care
about is the entry's stream map index, rather than the entry index
itself, so it's nice to have the iterator automatically assign the
former from the latter. Unfortunately, booting with KASAN reveals
the oversight that using a simple comma operator results in the
entry index being dereferenced before being checked for validity,
so we always access one element past the end of the fwspec array.

Flip things around so that the check always happens before the index
may be dereferenced.

Change-Id: Ifad076d88f51c8e27db3ae1208d70b0733800ce7
Fixes: adfec2e7 ("iommu/arm-smmu: Convert to iommu_fwspec")
Reported-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Git-commit: 8c82d6ec
Git-repo: https://source.codeaurora.org/quic/la/kernel/msm-4.4


Signed-off-by: Patrick Daly <pdaly@codeaurora.org>