drivers: net: xgene: uninitialized variable in xgene_enet_free_pagepool()

We never set "slots" in this function.

Fixes: a9380b0f

 ("drivers: net: xgene: Add support for Jumbo frame")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Iyappan Subramanian <isubramanian@apm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>