dmaengine: ioatdma: set the completion address register after channel reset

It seems that starting with Skylake Xeon, channel reset clears the
completion address register. Make sure the completion address register is
set again after reset.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>