ioat: remove chanerr mask setting for IOAT v3.x

The existing code set a value in the PCI_CHANERRMSK_INT register
for a workaround to address a pre-silicon bug on the Intel 5520 IO hub that
has been fixed when the hardware was released. There is no need for this
code.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Dan Williams <djbw@fb.com>