net: sxgbe: Fix waring for double kfree()

This patch fixes double kfree() calls at init_rx_ring() because
it causes static checker warning.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Byungho An <bh74.an@samsung.com>
Signed-off-by: Kukjin Kim <kgene@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>