async_tx: fix checking of dma_wait_for_async_tx() return value

dma_wait_for_async_tx() can also return DMA_PAUSED (which
should be considered as error).

Cc: Vinod Koul <vinod.koul@intel.com>
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>