staging: rtl8712: fix Prefer ether_addr_copy() over memcpy()

This patch fixes the following checkpatch.pl warning:
Prefer ether_addr_copy() over memcpy()
if the Ethernet addresses are __aligned(2)

pahole showed that the struct used pnetdev->dev_addr
is aligned to u16.

Moreover mac is a simple array, pdata is a pointer that
starts from an even offset.

Signed-off-by: Heba Aamer <heba93aamer@gmail.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>