dmaengine: mv_xor_v2: enable XOR engine after its configuration

The engine was enabled prior to its configuration, which isn't
correct. This patch relocates the activation of the XOR engine, to be
after the configuration of the XOR engine.

Fixes: 19a340b1 ("dmaengine: mv_xor_v2: new driver")
Cc: <stable@vger.kernel.org>
Signed-off-by: Hanna Hawa <hannah@marvell.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>