Fix uninitialized variable in __pci_osc_support_set().

If the ACPI namespace doesn't have any device object corresponding to
the specified hid, 'retval' in __pci_osc_support_set() is not changed
by the acpi_query_osc() callback. Since 'retval' is not initizlized in
the current implementation, the contents of 'retval' is undefined in
this case. This causes a mis-handling of ctrlset_buf[OSC_SUPPORT_TYPE]
and will cause an unexpected result in the subsequent
pci_osc_control_set() call as a result.
Signed-off-by: NKenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>