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

In the Linux kernel, the following vulnerability has been resolved:

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.