EDAC/i10nm: Use readl() to access MMIO registers

Instead of raw access, use readl() to access MMIO registers of
memory controller to avoid possible compiler re-ordering.

Fixes: d4dc89d0 ("EDAC, i10nm: Add a driver for Intel 10nm server processors")
Cc: <stable@vger.kernel.org>
Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>