ACPICA: ACPICA: add status check for acpi_hw_read before assigning return value

The value coming from acpi_hw_read() should not be used if it
returns an error code, so check the status returned by it before
using that value in two places in acpi_hw_register_read().

Reported-by: Mark Gross <mark.gross@intel.com>
Signed-off-by: Erik Schmauss <erik.schmauss@intel.com>
[ rjw: Changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>