staging: vt6656: Use ether_addr_copy() in vnt_fill_ieee80211_rts.

Both struct ieee80211_rts and struct ieee80211_hdr defined in
linux/ieee80211.h are declared as __aligned(2) so it is safe to use
ether_addr_copy() instead of memcpy().

Signed-off-by: Krzysztof Adamski <k@japko.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>