dmaengine: mv_xor: Fix a missing check in mv_xor_channel_add

dma_async_device_register() may fail and return an error. The capabilities
checked in mv_xor_channel_add() are not complete. The fix handles the
error by freeing the resources.

Signed-off-by: Aditya Pakki <pakki001@umn.edu>
Signed-off-by: Vinod Koul <vkoul@kernel.org>