RDMA/mlx5: Fix xlt_chunk_align calculation

The XLT chunk alignment depends on ent_size not sizeof(ent_size) aka
sizeof(size_t). The incoming ent_size is either 8 or 16, so the
miscalculation when 16 is required is only an over-alignment and
functional harmless.

Fixes: 8010d74b9965 ("RDMA/mlx5: Split the WR setup out of mlx5_ib_update_xlt()")
Link: https://lore.kernel.org/r/20210908081849.7948-2-schnelle@linux.ibm.com
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>