staging: r8188eu: remove intf_stop pointer

Remove the intf_stop pointer that points to a media-specific stop
function. The r8188eu driver supports only usb.

For usb drivers, intf_stop points to usb_intf_stop, which is only
two lines long.  We can remove intf_stop and usb_intf_stop and call
the two cancel functions directly.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Link: https://lore.kernel.org/r/20230206201800.139195-7-martin@kaiser.cx


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