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>

drivers/acpi/acpica/hwregs.c

@@ -528,13 +528,18 @@ acpi_status acpi_hw_register_read(u32 register_id, u32 *return_value)
 
 		status =
 		    acpi_hw_read(&value64, &acpi_gbl_FADT.xpm2_control_block);
+		if (ACPI_SUCCESS(status)) {
 			value = (u32)value64;
+		}
 		break;
 
 	case ACPI_REGISTER_PM_TIMER:	/* 32-bit access */
 
 		status = acpi_hw_read(&value64, &acpi_gbl_FADT.xpm_timer_block);
+		if (ACPI_SUCCESS(status)) {
 			value = (u32)value64;
+		}
+
 		break;
 
 	case ACPI_REGISTER_SMI_COMMAND_BLOCK:	/* 8-bit access */