dmaengine: mv_xor_v2: do not use descriptors not acked by async_tx

dmaengine: mv_xor_v2: do not use descriptors not acked by async_tx

commit bc473da1ed726c975ad47f8d7d27631de11356d8 upstream.

Descriptors that have not been acknowledged by the async_tx layer
should not be re-used, so this commit adjusts the implementation of
mv_xor_v2_prep_sw_desc() to skip descriptors for which
async_tx_test_ack() is false.

Fixes: 19a340b1a820 ("dmaengine: mv_xor_v2: new driver")
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>