ioat3: add missing DMA unmap to ioat_xor_val_self_test()

ioat3: add missing DMA unmap to ioat_xor_val_self_test()

Make ioat_xor_val_self_test() do DMA unmapping itself and fix handling
of failure cases.

Cc: Dan Williams <djbw@fb.com>
Cc: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Dan Williams <djbw@fb.com>
(cherry picked from commit 7369f56e3e7193583576ec705d95647b04838b05)

Orabug: 16495543

Signed-off-by: ethan.zhao <ethan.zhao@oracle.com>