vfio: add documentation for posted write argument

Signed-off-by: John Levon <john.levon@nutanix.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250616101314.3189793-1-john.levon@nutanix.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>
1 file changed