iommu/amd: Use atomic64_inc_return() in iommu.c

iommu/amd: Use atomic64_inc_return() in iommu.c

Use atomic64_inc_return(&ref) instead of atomic64_add_return(1, &ref)
to use optimized implementation and ease register pressure around
the primitive for targets that implement optimized variant.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Cc: Will Deacon <will@kernel.org>
Cc: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20241007084356.47799-1-ubizjak@gmail.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>