staging: rtl8192e: fix potential use after free

The variable skb is released via kfree_skb() when the return value of
_rtl92e_tx is not zero. However, after that, skb is accessed again to
read its length, which may result in a use after free bug. This patch
fixes the bug by moving the release operation to where skb is never
used later.

Signed-off-by: Pan Bian <bianpan2016@163.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/1572965351-6745-1-git-send-email-bianpan2016@163.com


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