iommu/arm-smmu-v3: Use str_read_write helper w/ logs

Adopt the `str_read_write` helper in event logging as suggested by the
coccinelle tool.

Signed-off-by: Pranjal Shrivastava <praan@google.com>
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Link: https://lore.kernel.org/all/20250107130053.GC6991@willie-the-truck/
Link: https://lore.kernel.org/r/20250107165100.1093357-1-praan@google.com


Signed-off-by: Will Deacon <will@kernel.org>