[PATCH v2 4/6] test/dmadev: check result for device stop

[Walsh, Conor]

> The DMA device stop API can return an error value so check that return
> value when running dmadev unit tests.
> 
> Signed-off-by: Bruce Richardson <bruce.richardson at intel.com>

Reviewed-by: Conor Walsh <conor.walsh at intel.com>