staging: rtl8188eu: use is_multicast_ether_addr

Use is_multicast_ether_addr instead of IS_MCAST.
By definition the broadcast address is also a multicast address,
so checking for !multicast in the conditional is sufficient.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>