staging: r8188eu: merge rtw_os_recvbuf_resource_free() into rtw_recv.c

staging: r8188eu: merge rtw_os_recvbuf_resource_free() into rtw_recv.c

The function rtw_os_recvbuf_resource_free() is just a wrapper around
usb_free_urb(). Call usb_free_urb() directly in
rtl8188eu_free_recv_priv() and remove rtw_os_recvbuf_resource_free()
to simplify the driver code.

Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20220807181538.8499-2-straube.linux@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>