at76c50x-usb: use ether_addr_equal_64bits

at76c50x-usb: use ether_addr_equal_64bits

Ether_addr_equal_64bits is more efficient than ether_addr_equal, and can be
used when each argument is an array within a structure that contains at
least two bytes of data beyond the array.

The structures involved are:
at76_priv defined in drivers/net/wireless/at76c50x-usb.h and
ieee80211_mgmt defined in include/linux/ieee80211.h

This was done using Coccinelle (http://coccinelle.lip6.fr/).

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: John W. Linville <linville@tuxdriver.com>