usb: gadget: configfs: simplify os_desc_item_to_gadget_info() helper

since os_desc_group is already a member of struct gadget_info,
we can simply just use container_of() to retrieve the latter,
without needing to dereference the cg_item's parent pointer.

use os_desc_item_to_gadget_info() helper in os_desc (un)link function.

Reviewed-by: Jack Pham <quic_jackp@quicinc.com>
Signed-off-by: Linyu Yuan <quic_linyyuan@quicinc.com>
Link: https://lore.kernel.org/r/1637211213-16400-2-git-send-email-quic_linyyuan@quicinc.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>