iommufd: Fix iommu_vevent_header tables markup

iommufd: Fix iommu_vevent_header tables markup

Stephen Rothwell reports htmldocs warnings on iommufd_vevent_header
tables:

Documentation/userspace-api/iommufd:323: ./include/uapi/linux/iommufd.h:1048: CRITICAL: Unexpected section title or transition.

------------------------------------------------------------------------- [docutils]
WARNING: kernel-doc './scripts/kernel-doc -rst -enable-lineno -sphinx-version 8.1.3 ./include/uapi/linux/iommufd.h' processing failed with: Documentation/userspace-api/iommufd:323: ./include/uapi/linux/iommufd.h:1048: (SEVERE/4) Unexpected section title or transition.

-------------------------------------------------------------------------

These are because Sphinx confuses the tables for section headings. Fix
the table markup to squash away above warnings.

Fixes: e36ba5ab808e ("iommufd: Add IOMMUFD_OBJ_VEVENTQ and IOMMUFD_CMD_VEVENTQ_ALLOC")
Link: https://patch.msgid.link/r/20250328114654.55840-1-bagasdotme@gmail.com
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Closes: https://lore.kernel.org/linux-next/20250318213359.5dc56fd1@canb.auug.org.au/
Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>