tests: edac: Ensure vars are not changed in assert evaluation

Coverity analysis reported following cases with side effect in assertion
(ASSERT_SIDE_EFFECT):

CID: 219574
CID: 219644
CID: 219659

Avoid issue by loading volatiles to local variables before assertion.

Fixes: #33079
Fixes: #33042
Fixes: #33030

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>