drivers: net: xgene: fix: Delete descriptor rings and buffer pools

xgene_enet_init_hw() should delete any descriptor rings and
buffer pools setup should le_ops->cle_init() return an error.

Signed-off-by: Iyappan Subramanian <isubramanian@apm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>