ACPICA: acpi_read: On error, do not modify the return value target location.

If an error happens in the middle of a split 32/32 64-bit I/O
operation, do not modify the target of the return value pointer.
Makes the code consistent with the rest of ACPICA. Bjorn Helgaas.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Reviewed-by: Len Brown <len.brown@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>