Avoid section type conflict in dma/ioat/dma_v3.c

Avoid section type conflict in dma/ioat/dma_v3.c

const __read_mostly is not legal and causes section type conflicts.
That's because the read.mostly section is not read only.
Simply drop the __read_mostly designation.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
[drop __read_mostly instead of const]
Signed-off-by: Dan Williams <dan.j.williams@intel.com>