hisi_acc_vfio_pci: Update migration data pointer correctly on saving/resume

hisi_acc_vfio_pci: Update migration data pointer correctly on saving/resume

[ Upstream commit be12ad45e15b5ee0e2526a50266ba1d295d26a88 ]

When the optional PRE_COPY support was added to speed up the device
compatibility check, it failed to update the saving/resuming data
pointers based on the fd offset. This results in migration data
corruption and when the device gets started on the destination the
following error is reported in some cases,

[  478.907684] arm-smmu-v3 arm-smmu-v3.2.auto: event 0x10 received:
[  478.913691] arm-smmu-v3 arm-smmu-v3.2.auto:  0x0000310200000010
[  478.919603] arm-smmu-v3 arm-smmu-v3.2.auto:  0x000002088000007f
[  478.925515] arm-smmu-v3 arm-smmu-v3.2.auto:  0x0000000000000000
[  478.931425] arm-smmu-v3 arm-smmu-v3.2.auto:  0x0000000000000000
[  478.947552] hisi_zip 0000:31:00.0: qm_axi_rresp [error status=0x1] found
[  478.955930] hisi_zip 0000:31:00.0: qm_db_timeout [error status=0x400] found
[  478.955944] hisi_zip 0000:31:00.0: qm sq doorbell timeout in function 2

Fixes: d9a871e4a143 ("hisi_acc_vfio_pci: Introduce support for PRE_COPY state transitions")
Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20231120091406.780-1-shameerali.kolothum.thodi@huawei.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>