vfio/mlx5: Rename some stuff to match chunk mode

vfio/mlx5: Rename some stuff to match chunk mode

Upon chunk mode there may be multiple images that will be read from the
device upon STOP_COPY.

This patch is some preparation for that mode by replacing the relevant
stuff to a better matching name.

As part of that, be stricter to recognize PRE_COPY error only when it
didn't occur on a STOP_COPY chunk.

Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20230911093856.81910-6-yishaih@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>