staging: rtl8723bs: Change type of rtw_os_recvbuf_resource_free()

Change return type of function rtw_os_recvbuf_resource_free to void as
its return value is never stored, checked or otherwise used.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>