staging:rtl8192u: Rename member variables - Style

Rename the member variables of union aci_aifsn, which should be named
in lowercase. The only member variable, of this union, which is
actually used is 'acm'.

This are coding style changes 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>