staging:rtl8192u: Remove unused union AC_PARAM - Style

The union ACM_PARAM is never actually used in code so removed. This
is a coding style change which should have no impact on runtime code
execution.

Signed-off-by: John Whitmore <johnfwhitmore@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>