ethernet: atheros: fix a memleak in atl1e_setup_ring_resources

In the error handling of 'offset > adapter->ring_size', the
tx_ring->tx_buffer allocated by kzalloc should be freed,
instead of 'goto failed' instantly.

Fixes: a6a53252

 ("atl1e: Atheros L1E Gigabit Ethernet driver")
Signed-off-by: Zhipeng Lu <alexious@zju.edu.cn>
Reviewed-by: Suman Ghosh <sumang@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>