staging: rtl8192u: release memory on error path

In rtl819xU_tx_cmd if usb_submit_urb fails the allocated memories should
be released.

Signed-off-by: Navid Emamdoost <navid.emamdoost@gmail.com>
Link: https://lore.kernel.org/r/20190920014303.31410-1-navid.emamdoost@gmail.com


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