Staging: rtl8192u: Use BIT macro

Use BIT macro, as kernel provides the macro for improving uniform
and more readable way to define these constants.

Issue suggested by Coccinelle.

Signed-off-by: Madhumitha Prabakaran <madhumithabiw@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>