xen/arm: smmuv3: Fix fall-through warning for Clang

xen/arm: smmuv3: Fix fall-through warning for Clang

Backport Linux commit 5a1ab5c0299a. This is the clean backport without
any changes.

Fix the following fallthrough warning (arm64-randconfig with Clang):

drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c:382:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]

Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/lkml/60edca25.k00ut905IFBjPyt5%25lkp@intel.com/
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Origin: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 5a1ab5c0299a
Signed-off-by: Rahul Singh <rahul.singh@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>