Atheros, atl2: Fix mem leaks in error paths of atl2_set_eeprom

We leak in some error paths of drivers/net/atlx/atl2.c:atl2_set_eeprom().
The memory allocated to 'eeprom_buff' is not freed when we return -EIO.
This patch fixes that up and also removes a pointless explicit cast.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: David S. Miller <davem@davemloft.net>