staging: r8188eu: use skb_put_data instead of skb_put/memcpy pair

skb_put_data is shorter and clear.

Signed-off-by: Ivan Safonov <insafonov@gmail.com>
Link: https://lore.kernel.org/r/20190901195301.GA16043@alpha


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