tools/testing/cxl: Use injected poison for get poison list

Prior to poison inject support, the mock of 'Get Poison List'
returned a poison list containing a single mocked error record.

Following the addition of poison inject and clear support to the
mock driver, use the mock_poison_list[], rather than faking an
error record. Mock_poison_list[] list tracks the actual poison
inject and clear requests issued by userspace.

Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/0f4242c81821f4982b02cb1009c22783ef66b2f1.1681874357.git.alison.schofield@intel.com


Signed-off-by: Dan Williams <dan.j.williams@intel.com>