Staging: rtl8192u: Fix do not use // c99 comments.

This patch fixes "do not use // C99 comments" errors in
r8190_rtl8256.h

Signed-off-by: Dilek Uzulmez <dilekuzulmez@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>