dmaengine: idxd: Fix clobbering of SWERR overflow bit on writeback

Current code blindly writes over the SWERR and the OVERFLOW bits. Write
back the bits actually read instead so the driver avoids clobbering the
OVERFLOW bit that comes after the register is read.

Fixes: bfe1d560 ("dmaengine: idxd: Init and probe for Intel data accelerators")
Reported-by: Sanjay Kumar <sanjay.k.kumar@intel.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/161352082229.3511254.1002151220537623503.stgit@djiang5-desk3.ch.intel.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>