iommu/riscv: Remove overflows on the invalidation path

iommu/riscv: Remove overflows on the invalidation path

Since RISC-V supports a sign extended page table it should support
a gather->end of ULONG_MAX, but if this happens it will infinite loop
because of the overflow.

Also avoid overflow computing the length by moving the +1 to the other
side of the <

Fixes: 488ffbf18171 ("iommu/riscv: Paging domain support")
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>