staging:rtl8192u: Remove union from aci_aifsn - Style

The union aci_aifsn is not used as a union, but only as a struct.
The union seems to have been used to ensure that the size of the
structure was only a single byte. That size is set by the bitfield
structure, adding a union with an unused byte adds nothing.

The union has been removed. This is a coding style change and
should not impact runtime code execution.

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