From: Leon Romanovsky <leonro@xxxxxxxxxx>
nvme_map_data() is called when request has physical segments, hence
the nvme_unmap_data() should have same condition to avoid dereference.
Fixes: 4aedb705437f ("nvme-pci: split metadata handling from nvme_map_data / nvme_unmap_data")
Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxx>
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