ACPI/PCI: Reorder checks in acpi_pci_osc_control_set()

Make acpi_pci_osc_control_set() attempt to find the handle of the
_OSC object under the given PCI root bridge object after verifying
that its second argument is correct and that there is a struct
acpi_pci_root object for the given root bridge handle, which is
more logical than the old code.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Reviewed-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>