docs: ABI: fix documentation warning in sysfs-driver-mlxreg-io

The use of a Sphinx list within this ABI file caused the following warning:

  Documentation/ABI/stable/sysfs-driver-mlxreg-io:230: WARNING: Unexpected indentation.
  Documentation/ABI/stable/sysfs-driver-mlxreg-io:230: WARNING: Block quote ends without a blank line; unexpected unindent.

Remove the bullets to make the warning go away and get proper formatting.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>