dmatest: correct raid6 PQ test

The number of PQ sources specified by module parameter "pq_sources"
is always forced odd to fit into dmatest's destination verificaton
scheme. But number of PQ sources and coefficients as passed to the
driver's prep_dma_pq() is not adjusted accordingly.

Fix it now to get correct PQ testing results in the case passed
"pq_sources" parameter is even.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Maciej Sosnowski <maciej.sosnowski@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>