ACPI/PCI: Remove surplus parentheses from a return statement

Remove unnecessary parentheses enclosing the value in a return
statement in the drivers/acpi/pci_link.c.

Signed-off-by: Krzysztof Wilczynski <kw@linux.com>
Reviewed-by: Andrew Murray <andrew.murray@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>