The code to handle cloned skb overwriting is unnecessary in the
sky2 driver and is buggy. The bug is that pskb_expand_head can change the
skb but the driver has already mapped in the header.

Since the sky2 hardware doesn't need to overwrite memory, the buggy
code can just be removed; it was mistakenly copied from the tg3
driver.
Signed-off-by: NStephen Hemminger <shemminger@osdl.org>
Signed-off-by: NJeff Garzik <jeff@garzik.org>