staging: rtl8712: Use ether_addr_copy() instead of memcpy()

Fixes Warning encounter this by applying checkpatch.pl against this file:
Prefer ether_addr_copy() over memcpy() if the Ethernet addresses
are __aligned(2)

pahole output for respective structures:
- addr->sa_data
struct sockaddr {
	sa_family_t                sa_family;            /*     0     2 */
	char                       sa_data[14];          /*     2    14 */

	/* size: 16, cachelines: 1, members: 2 */
	/* last cacheline: 16 bytes */
};

- pnetdev->dev_addr
dev_addr is interface address infor from generic net_device structure
which is properly aligned and have some patches with this change as well.
"staging: rtl8712: fix Prefer ether_addr_copy() over memcpy()"
(sha1: 36e4d882)

Signed-off-by: Jagan Teki <jteki@openedev.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Florian Schilhabel <florian.c.schilhabel@googlemail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>