ACPI: bus: Fix the _OSC capability check for FFH OpRegion

As per the ACPI specification(vide section Platform-Wide OSPM Capabilities)
the OSPM must set this bit to indicate support for the usage of Functional
Fixed Hardware (FFixedHW) Operation Regions rather than the firmware as
expected in the code.

Update the check accordingly to reflect the requirement as stated in the
specification.

Reported-by: Jose Marinho <jose.marinho@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>