ACPI: optimize pci_rootbridge search

acpi_get_pci_rootbridge_handle() walks the ACPI name space
searching for seg, bus and the PCI_ROOT_HID_STRING --
returning the handle as soon as if find the match.

But the current codes always parses through the whole namespace because
the user_function find_pci_rootbridge() returns status=AE_OK when it finds the match.

Make the find_pci_rootbridge() return AE_CTRL_TERMINATE when it finds the match.
This reduces the ACPI namespace walk for acpi_get_pci_rootbridge_handle().

Signed-off-by: Justin Chen <justin.chen@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>